user-1: Q:

Did the Buddha copy Hinduism and add his own stuff? Why is Buddhism
  connected to thoughts in Hinduism if he didn't do so?


user17298: Buddha used ideas common to the Indian spiritual circles of his time, including Hinduism, but was far from simply copying them. Some of these ideas he strongly opposed, like the one of eternal atman. Some of them he included into his teachings, like karma/kamma, but gave it different meaning, more in line with his stressing importance of ethical quality of our intentions and subsequently our actions.

user16223: In his introduction to the translation of the early upanishads, Patrick Olivelle writes-

The Upanisads were composed at a time of great social, economic, and religious change; they document the transition from the archaic ritualism of the Veda into new religious ideas and institutions. It is in them that we note for the first time the emergence of central religious concepts of both Hinduism and of the new religious movements, such as Buddhism and Jainism, that emerged not long after the composition of the early Upanisads. Such concepts include the doctrine of re-birth, the law of karma that regulates the rebirth process, and the techniques of liberation from the cycle of rebirth, such as mental training associated with Yoga, ascetic self-denial and mortification, and the renunciation of sex, wealth, and family
  life. Even though theoretically the whole of the vedic corpus is accepted as revealed truth, in reality it is the Upanisads that have continued to influence the life and
  thought of the various religious traditions that we have come to call Hindu. Upanisads are the scriptures par excellence of Hinduism.

Some of Buddhism's cardinal doctrines like karma, reincarnation and ahimsa, compassion are found in the pre-Buddhistic early upanishads. 
First, let us take the Brihadaranyaka upanishad. Regarding the date of this upanishad, the following are the opinions of most scholars - 
https://en.m.wikipedia.org/wiki/Brihadaranyaka_Upanishad

The exact year, and even the century of the Upanishad composition is unknown. Scholars have offered different estimates ranging from 900 BCE to 600 BCE, all preceding Buddhism. Brihadaranyaka is one of the first Upanishads, along with that of Jaiminiya Upanishad and Chandogya Upanishads.[13][14] The Brihadaranyaka Upanishad was in all likelihood composed in the earlier part of 1st millennium BCE, around 700 BCE, give or take a century or so, according to Patrick Olivelle.[11] It is likely that the text was a living document and some verses were edited over a period of time before the 6th century BCE.[13]

Thus, this upanishad was before the time of the Buddha, as per almost all scholarly opinions. 
Further, there are about five pre-Buddhistic upanishads, according to scholars, and the Brihadaranyaka is one of them.
https://en.m.wikipedia.org/wiki/Upanishads

The early Upanishads all predate the Common Era, five[note 6] of them in all likelihood pre-Buddhist (6th century BCE),[18]
[note 6] The pre-Buddhist Upanishads are: Brihadaranyaka, Chandogya, Kaushitaki, Aitareya, and Taittiriya Upanishads.[18]

Death and transmigration have been described in the Brihadaranyaka upanishad -
https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc122058.html
I am referring to the above link only for the Sanskrit text. I will give translation of Patrick Olivelle in order to remove any possible accusations of hindu bias.

.....tena pradyotenaiṣa ātmā niṣkrāmati—cakśuṣṭo vā, mūrdhno vā, anyebhyo vā śarīradeśebhyaḥ; tamutkrāmantaṃ prāṇo'nūtkrāmati; prāṇamanūtkrāmantaṃ sarve prāṇā anūtkrāmanti; savijñāno bhavati, savijñānamevānvavakrāmati । taṃ vidyākarmaṇī samanvārabhete pūrvaprajñā ca || 2 ||

Here I am giving Patrick Olivelle's translation (not from the above link).

Then the top of his heart lights up, and with that light the
  self exits through the eye or the head or some other part of the body. As he is de-parting, his lifebreath (prana) departs with him. And as his lifebreath departs, all his vital functions (prana) depart with it.
  He then descends into a state of mere awareness and develops into one who is thus endowed with perception. Then learning and rites, as well as memory, take
  hold of him.
tadyathā tṛṇajalāyukā tṛṇasyāntaṃ gatvānyamākramamākramyātmānamupasaṃharati, evamevāyamātmedaṃ śarīraṃ nihatya, avidyāṃ gamayitvā, anyamākramamākramyātmānamupasaṃharati || 3 ||
tadyathā peśaskārī peśaso mātrām apādāyānyannavataraṃ kalyāṇataraṃ rūpaṃ tanute, evamevāyamātmedaṃ śarīraṃ nihatya, avidyāṃ gamayitvā, anyannavataraṃ kalyāṇataraṃ rūpaṃ kurute—pitryaṃ vā, gāndharvaṃ vā daivaṃ vā, prājāpatyaṃ vā, brāhmaṃ vā, anyeṣāṃ vā bhūtānām || 4 ||

Olivelle's translation again -

"It is like this. As a caterpillar, when it comes to the tip of a blade of grass, reaches out to a new foothold and draws itself onto it, so the self (atman), after it has knocked down this body and rendered it unconscious, reaches out to a new foothold and draws itself onto it.
"It is like this. As a weaver, after she has removed the colored yarn, weaves a different design that is newer and more attractive, so the self, after it has knocked
  down this body and rendered it unconscious, makes for himself a different figure that is newer and more attractive—the figure of a forefather, or of a Gandharva, or
  of a god, or of Prajapati, or of brahman, or else the figure of some other being.

Now, let us look at a different section of the upanishad -
https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc120049.html

tadyathānaḥ susamāhitamutsarjadyāyāt, evamevāyaṃ śārīra ātmā prājñenātmanānvārūḍha utsarjanyāti, yatraitadūrdhvocchvāsī bhavati || 35 ||
sa yatrāyamaṇimānaṃ nyeti—jarayā vopatapatā vāṇimānaṃ nigacchati—tadyathāmraṃ vodumbaraṃ vā pippalaṃ vā bandhanātpramucyate, evamevāyaṃ puruṣa ebhyo'ṅgebhyaḥ saṃpramucya punaḥ pratinyāyaṃ pratiyonyādravati prāṇāyaiva || 36 ||

Patrick Olivelle's translation - 

"It is like this. As a heavily loaded cart goes along creaking, so this bodily self (atman), saddled with the self (atman) of knowledge, goes along groaning as he is breathing his last.
   36
   Now a man grows feeble on account of either old age or
  sickness. "It is like this. As a mango or a fig or a berry detaches itself from its stem, so this person frees himself from these bodily parts and rushes along the same path and through the same opening back again to a new life (prana).

The above quotes show that the doctrine of reincarnation is present in the pre-Buddhistic brihadaranyaka upanishad. 
Now, let us come to the doctrine of karma in the same upanishad. (The bold highlighted Sanskrit below shows that the exact word karma was used in this upanishad. So not only is the doctrine of karma found here, but also the exact word karma was used to describe the doctrine).
https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc122058.html

yathākārī yathācārī tathā bhavati—sādhukārī sādhurbhavati, pāpakārī pāpo bhavati; puṇyaḥ puṇyena karmaṇā bhavati, pāpaḥ pāpena | atho khalvāhuḥ kāmamaya evāyaṃ puruṣa iti; sa yathākāmo bhavati tatkraturbhavati, yatkraturbhavati tatkarma kurute, yatkarma kurute tadabhisaṃpadyate || 5 ||
tadeṣa śloko bhavati |
                tadeva saktaḥ saha karmaṇaiti
                liṅgaṃ mano yatra niṣaktamasya |
            prāpyāntaṃ karmaṇastasya yatkiñceha karotyayam |
            tasmāllokātpunaraityasmai lokāya karmaṇe ||
        iti nu kāmayamānaḥ; athākāmayamānaḥ—yo'kāmo
  niṣkāma āptakāma ātmakāmo na tasya prāṇā utkrāmanti,
  brahmaiva sanbrahmāpyeti || 6 ||
What a man turns out to be depends on how he
  acts and on how he conducts himself. If his actions are good, he will turn into something good. If his actions are bad, he will turn into something bad. A man turns
  into something good by good action and into something bad by bad action. And so people say: 'A person here consists simply of desire.' A man resolves in accordance
  with his desire, acts in accordance with his resolve, and turns out to be in accordance with his action.
On this point there is the following verse:
  A man who's attached goes with his action,
  to that very place to which
  his mind and character cling.
  Reaching the end of his action,
  of whatever he has done in this world—
  From that world he returns
  back to this world,
  back to action.
  "That is the course of a man who desires.

A different translation is given in wikipedia, but the essence is similar.
https://en.m.wikipedia.org/wiki/Brihadaranyaka_Upanishad#Karma_theory

One of the earliest formulation of the Karma doctrine occurs in the Brihadaranyaka Upanishad.[46] For example:
Now as a man is like this or like that,
  according as he acts and according as he behaves, so will he be;
  a man of good acts will become good, a man of bad acts, bad;
  he became pure by pure deeds, bad by bad deeds;
And here they say that a person consists of desires,
  and as is his desire, so is his will;
  and as is his will, so is his deed;
  and whatever deed he does, that he will reap.
— Brihadaranyaka Upanishad, Hymns 4.4.5-4.4.6[48][49]

Another instance of the doctrine of karma in the same upanishad - 
https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc118304.html

....tau hotkramya mantrayāṃcakrāte; tau ha yadūcatuḥ karma haiva tadūcatuḥ, atha yatpraśaśaṃsatuḥ karma haiva tat praśaśaṃsatuḥ; puṇyo vai puṇyena karmaṇā bhavati, pāpaḥ pāpeneti | tato ha jāratkārava ārtabhāga upararāma || 13 ||

Patrick Olivelle's translation - 

So they left and talked about it. And what did they talk about?—they talked about nothing but action. And what did they praise?—they praised nothing but action. Yajnavalkya told him: "A man turns into something good by good action and into something bad by bad action."

It has been shown above that two of the cardinal doctrines of buddhism - karma and reincarnation - are already present in the pre-Buddhistic upanishads. 
PS: This can become a long post, so I will either write a separate answer for other points or will extend this later.

user471: What was before the Buddha? The Vedas and the earliest Upanishads (Brhadaranyaka, Chandogya) came before the Buddha.
A few other Upanishads (Taittiriya, Aitareya, and Kausitaki) and the Nyaya school of logic may have developed around the same time as the Buddha.
If you look at the scholarly dates given in Wikipedia, all Vedanta schools, Samkhya, Yogasutras of Patanjali, Purva Mimamsa school, the rest of the Upanishads (Kena, Katha, Isa, Svetasvatara, Mundaka, Prasna, Mandukya), Brahmasutras and Bhagavad Gita all came after the Buddha's time.
The closest Hindu school of philosophy to Buddhism, appears to be Advaita Vedanta. Gaudapada and Adi Shankara who founded Advaita Vedanta lived around 6th to 7th century CE. The Buddha lived over a thousand years earlier.
I imagined that Advaita Vedanta influenced Indian Mahayana schools, but it turns out that it may be the other way round. Nagarjuna, the founder of the Madhyamaka school, lived around 150 - 250 CE. Asanga and Vasubandhu, the founders of the Yogacara school, lived around 3rd to 4th century CE.
All this info can be found in Wikipedia.
So, who copied who?

The Buddha certainly used terms like karma and dharma from the culture around him, but he redefined those terms based on his teachings.
Let me give you an example. The term "karma" (which simply means action) originates from the Brhadaranyaka Upanishad that predates the Buddha by at least a century. It introduces the idea that doing good makes you good and brings good results, and vice versa.
Later, the Bhagavad Gita (in chapters 2 and 3), which comes 2 centuries after the Buddha, says that the dharma (here meaning duty) of a warrior is to fight for a just cause. If a warrior fights and kills another, while performing his duty, but does so as a sacrifice or offering to God, without any kind of attachment, including to the fruits of action, then the warrior will be freed from sin. On the other hand, if he shirks his responsibility and duty, he would incur sin. This is called karma yoga, which is the title of chapter 3.
On the other hand, in Buddhism, karma is always related to an individual's intention which starts as a thought but is later manifested and exerted through thoughts and actions. The intention is the most important thing. 
From the AN 6.63:

"Intention, I tell you, is kamma. Intending, one does kamma by way of
  body, speech, & intellect."

In SN 42.3, a warrior asks the Buddha whether he would go to heavan if he dies in battle. The Buddha states that he would instead be reborn in hell because of exerting the intention to violently kill another human being. It's all about the mind. Please also see this answer. Killing because of duty violates the first precept. Pure self-defense may be acceptable for lay people, though.
The term dharma could mean righteousness, duty, order, religion in Hindu texts. In Buddhism, the term dharma or dhamma could mean teachings, phenomena, complex mental concepts. It's slightly different, but related.
With these examples it should be clear that although Hinduism and Buddhism share the terms karma and dharma, they are actually not quite the same.

One thing is clear. Anatta or Anatman is uniquely Buddhist, and it clearly separates all Hindu philosophy from Buddhism. There can be no Vedanta without Atman, and there can be no Buddhism without Anatman.

user8157: 'Hinduism' did not exist when the Buddha was alive, as follows from Wikipedia:

This "Hindu synthesis" started to develop between 500 BCE and 300
  CE, after the end of the Vedic period (1500 to 500 BCE), and
  flourished in the medieval period, with the decline of Buddhism in
  India
Wkipedia: Hinduism

When Buddha was alive, the religion of the Brahmin priests we call 'Brahmanism', which was far more limited in scope than Hinduism, per the stock description from the Pali suttas below:

Now at that time the brahmin...had mastered the Three Vedas, together
  with their vocabularies, ritual, phonology and etymology and the
  testament as fifth. He knew philology and grammar, and was well versed
  in cosmology and the marks of a great man.
MN 91

The Three Vedas are explained in Wikipedia as follows:

The canonical division of the Vedas is fourfold (turīya) viz.,

Rigveda (RV)
Yajurveda (YV, with the main division TS vs. VS) 
Samaveda (SV)
Atharvaveda (AV)

Of these, the first three were the principal original division, also
  called "trayī vidyā"; that is, "the triple science" of reciting hymns
  (Rigveda), performing sacrifices (Yajurveda) and chanting songs
  (Samaveda). The Rigveda is the oldest work, which Witzel
  states are probably from the period of 1900 to 1100 BCE. Witzel, also
  notes that it is the Vedic period itself, where incipient lists divide
  the Vedic texts into three (trayī) or four branches: Rig, Yajur, Sama
  and Atharva
Wiki

If you read the Brāhmaṇa Vagga in the Majjhima Nikaya, there was no Hinduism. In fact, Hinduism, as inferred by Wikipedia (in the 1st quote above), probably copied from Buddhism. 
For example (while I am happy to be corrected), I do not recall reading in the Pali suttas any detailed discussion/debate between the Brahmins & the Buddha about respective theories/doctrines of karma & reincarnation. In the little I researched, I found no systematic doctrine of karma & reincarnation in the Three Vedas. Even when I browsed some later 'Upanishads', I found no mature systematic doctrine about karma & reincarnation (apart from the ideas of one certain individual philosopher). 
Again, if we read the Brāhmaṇa Vagga in the Majjhima Nikaya, we find the Brahmins were similar to the Hebrews (and probably many other tribal groups), where their belief system was about how they were 'God's chosen people' or 'born from Brahma's mouth/breath' (while the other castes were born from lesser parts of Brahma's body).
Some useful links from Sutta Central, with lots of links, books & research, are:

The early Upanishads: a nice introduction to the pre-Buddhist tradition
Rebirth & reincarnation in the Brahman Vedas

Note: While the Pali suttas never mention the 'Upanishads', the reincarnation orientated leader of Sutta Central, namely, Bhikkhu Sujato, appears intent to follow conventional historians rather than follow the Pali suttas, in his efforts to back-date the Upanishads to prior to Buddhism. If we place our trust in the Pali suttas, we find what existed prior to the Buddha was the Three Vedas & their accompaniments. 
An answer about this topic by Bhikkhu Yuttadhammo is here: Did the Buddha ever mention the Upanishads or the Vedas?
Lastly, if you wish to be a real Buddhist, it is not possible to believe the Buddha copied any of his core teachings from Brahmanism/Hinduism because the suttas say what the Buddha taught he "never heard before". "A Buddha" cannot copy other doctrines otherwise he/she cannot be called "A Perfectly Self-Enlightened Buddha" ("Sammasambuddha"). 

'Arising, arising!' — At this thought, monks, there arose in me,
  concerning things unheard of before, vision, knowledge, understanding,
  light.
'Cessation, cessation!' — At this thought, monks, there arose in me,
  concerning things unheard of before, vision, knowledge, understanding,
  light."
SN 12.10

Vision arose, insight arose, discernment arose, knowledge arose, illumination arose within me with regard to things never heard before:
Dhammacakkappavattana Sutta


-1: <p>Q:</p>

<blockquote>
  <p>Did the Buddha copy Hinduism and add his own stuff? Why is Buddhism
  connected to thoughts in Hinduism if he didn't do so?</p>
</blockquote>
 17298: <p>Buddha used ideas common to the Indian spiritual circles of his time, including Hinduism, but was far from simply copying them. Some of these ideas he strongly opposed, like the one of eternal atman. Some of them he included into his teachings, like karma/kamma, but gave it different meaning, more in line with his stressing importance of ethical quality of our intentions and subsequently our actions.</p>
 16223: <p>In his <a href="https://rads.stackoverflow.com/amzn/click/com/0195124359" rel="nofollow noreferrer" rel="nofollow noreferrer">introduction to the translation of the early upanishads,</a> Patrick Olivelle writes-</p>

<blockquote>
  <p>The Upanisads were composed at a time of great social, economic, and religious change; they document the transition from the archaic ritualism of the Veda into new religious ideas and institutions. <strong>It is in them that we note for the first time the emergence of central religious concepts of both Hinduism and of the new religious movements, such as Buddhism and Jainism, that emerged not long after the composition of the early Upanisads. Such concepts include the doctrine of re-birth, the law of karma that regulates the rebirth process, and the techniques of liberation from the cycle of rebirth, such as mental training associated with Yoga, ascetic self-denial and mortification, and the renunciation of sex, wealth, and family
  life.</strong> Even though theoretically the whole of the vedic corpus is accepted as revealed truth, in reality it is the Upanisads that have continued to influence the life and
  thought of the various religious traditions that we have come to call Hindu. <strong>Upanisads are the scriptures par excellence of Hinduism.</strong></p>
</blockquote>

<p>Some of Buddhism's cardinal doctrines like karma, reincarnation and ahimsa, compassion are found in the pre-Buddhistic early upanishads. </p>

<p>First, let us take the Brihadaranyaka upanishad. Regarding the date of this upanishad, the following are the opinions of most scholars - </p>

<p><a href="https://en.m.wikipedia.org/wiki/Brihadaranyaka_Upanishad" rel="nofollow noreferrer">https://en.m.wikipedia.org/wiki/Brihadaranyaka_Upanishad</a></p>

<blockquote>
  <p>The exact year, and even the century of the Upanishad composition is unknown. Scholars have offered different estimates ranging from 900 BCE to 600 BCE, all preceding Buddhism. Brihadaranyaka is one of the first Upanishads, along with that of Jaiminiya Upanishad and Chandogya Upanishads.[13][14] The Brihadaranyaka Upanishad was in all likelihood composed in the earlier part of 1st millennium BCE, around 700 BCE, give or take a century or so, according to Patrick Olivelle.[11] It is likely that the text was a living document and some verses were edited over a period of time before the 6th century BCE.[13]</p>
</blockquote>

<p>Thus, this upanishad was before the time of the Buddha, as per almost all scholarly opinions. </p>

<p>Further, there are about five pre-Buddhistic upanishads, according to scholars, and the Brihadaranyaka is one of them.</p>

<p><a href="https://en.m.wikipedia.org/wiki/Upanishads" rel="nofollow noreferrer">https://en.m.wikipedia.org/wiki/Upanishads</a></p>

<blockquote>
  <p>The early Upanishads all predate the Common Era, five[note 6] of them in all likelihood pre-Buddhist (6th century BCE),[18]</p>
  
  <p>[note 6] The pre-Buddhist Upanishads are: Brihadaranyaka, Chandogya, Kaushitaki, Aitareya, and Taittiriya Upanishads.[18]</p>
</blockquote>

<p>Death and transmigration have been described in the Brihadaranyaka upanishad -</p>

<p><a href="https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc122058.html" rel="nofollow noreferrer">https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc122058.html</a></p>

<p><strong>I am referring to the above link only for the Sanskrit text. I will give translation of Patrick Olivelle in order to remove any possible accusations of hindu bias.</strong></p>

<blockquote>
  <p>.....tena pradyotenaiṣa ātmā niṣkrāmati—cakśuṣṭo vā, mūrdhno vā, anyebhyo vā śarīradeśebhyaḥ; tamutkrāmantaṃ prāṇo'nūtkrāmati; prāṇamanūtkrāmantaṃ sarve prāṇā anūtkrāmanti; savijñāno bhavati, savijñānamevānvavakrāmati । taṃ vidyākarmaṇī samanvārabhete pūrvaprajñā ca || 2 ||</p>
</blockquote>

<p>Here I am giving Patrick Olivelle's translation (not from the above link).</p>

<blockquote>
  <p>Then the top of his heart lights up, and with <strong>that light the
  self exits through the eye or the head or some other part of the body</strong>. As he is de-parting, his lifebreath (prana) departs with him. And as his lifebreath departs, all his vital functions (prana) depart with it.
  <strong>He then descends into a state of mere awareness and develops into one who is thus endowed with perception.</strong> Then learning and rites, as well as memory, take
  hold of him.</p>
  
  <p>tadyathā tṛṇajalāyukā tṛṇasyāntaṃ gatvānyamākramamākramyātmānamupasaṃharati, evamevāyamātmedaṃ śarīraṃ nihatya, avidyāṃ gamayitvā, anyamākramamākramyātmānamupasaṃharati || 3 ||</p>
  
  <p>tadyathā peśaskārī peśaso mātrām apādāyānyannavataraṃ kalyāṇataraṃ rūpaṃ tanute, evamevāyamātmedaṃ śarīraṃ nihatya, avidyāṃ gamayitvā, anyannavataraṃ kalyāṇataraṃ rūpaṃ kurute—pitryaṃ vā, gāndharvaṃ vā daivaṃ vā, prājāpatyaṃ vā, brāhmaṃ vā, anyeṣāṃ vā bhūtānām || 4 ||</p>
</blockquote>

<p>Olivelle's translation again -</p>

<blockquote>
  <p>"It is like this. As a caterpillar, when it comes to the tip of a blade of grass, reaches out to a new foothold and draws itself onto it, <strong>so the self (atman), after it has knocked down this body and rendered it unconscious, reaches out to a new foothold and draws itself onto it.</strong></p>
  
  <p>"It is like this. As a weaver, after she has removed the colored yarn, weaves a different design that is newer and more attractive, <strong>so the self, after it has knocked
  down this body and rendered it unconscious, makes for himself a different figure that is newer and more attractive—the figure of a forefather, or of a Gandharva, or
  of a god, or of Prajapati, or of brahman, or else the figure of some other being.</strong></p>
</blockquote>

<p>Now, let us look at a different section of the upanishad -</p>

<p><a href="https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc120049.html" rel="nofollow noreferrer">https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc120049.html</a></p>

<blockquote>
  <p>tadyathānaḥ susamāhitamutsarjadyāyāt, evamevāyaṃ śārīra ātmā prājñenātmanānvārūḍha utsarjanyāti, yatraitadūrdhvocchvāsī bhavati || 35 ||</p>
  
  <p>sa yatrāyamaṇimānaṃ nyeti—jarayā vopatapatā vāṇimānaṃ nigacchati—tadyathāmraṃ vodumbaraṃ vā pippalaṃ vā bandhanātpramucyate, evamevāyaṃ puruṣa ebhyo'ṅgebhyaḥ saṃpramucya punaḥ pratinyāyaṃ pratiyonyādravati prāṇāyaiva || 36 ||</p>
</blockquote>

<p>Patrick Olivelle's translation - </p>

<blockquote>
  <p>"It is like this. As a heavily loaded cart goes along creaking, so this bodily self (atman), saddled with the self (atman) of knowledge, goes along groaning as he is breathing his last.
   36
   Now a man grows feeble on account of either old age or
  sickness. "It is like this. As a mango or a fig or a berry detaches itself from its stem, <strong>so this person frees himself from these bodily parts and rushes along the same path and through the same opening back again to a new life (prana).</strong></p>
</blockquote>

<p>The above quotes show that the doctrine of reincarnation is present in the pre-Buddhistic brihadaranyaka upanishad. </p>

<p>Now, let us come to the doctrine of karma in the same upanishad. (The bold highlighted Sanskrit below shows that the exact word karma was used in this upanishad. So not only is the doctrine of karma found here, but also the exact word karma was used to describe the doctrine).</p>

<p><a href="https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc122058.html" rel="nofollow noreferrer">https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc122058.html</a></p>

<blockquote>
  <p>yathākārī yathācārī tathā bhavati—sādhukārī sādhurbhavati, pāpakārī pāpo bhavati; puṇyaḥ puṇyena <strong>karmaṇā</strong> bhavati, pāpaḥ pāpena | atho khalvāhuḥ kāmamaya evāyaṃ puruṣa iti; sa yathākāmo bhavati tatkraturbhavati, yatkraturbhavati tat<strong>karma</strong> kurute, yat<strong>karma</strong> kurute tadabhisaṃpadyate || 5 ||</p>
  
  <p>tadeṣa śloko bhavati |
                tadeva saktaḥ saha <strong>karmaṇaiti</strong>
                liṅgaṃ mano yatra niṣaktamasya |
            prāpyāntaṃ <strong>karmaṇastasya</strong> yatkiñceha karotyayam |
            tasmāllokātpunaraityasmai lokāya <strong>karmaṇe</strong> ||
        iti nu kāmayamānaḥ; athākāmayamānaḥ—yo'kāmo
  niṣkāma āptakāma ātmakāmo na tasya prāṇā utkrāmanti,
  brahmaiva sanbrahmāpyeti || 6 ||</p>
  
  <p><strong>What a man turns out to be depends on how he
  acts and on how he conducts himself.</strong> If his actions are good, he will turn into something good. If his actions are bad, he will turn into something bad. <strong>A man turns
  into something good by good action and into something bad by bad action.</strong> And so people say: 'A person here consists simply of desire.' A man resolves in accordance
  with his desire, acts in accordance with his resolve, and turns out to be in accordance with his action.</p>
  
  <p>On this point there is the following verse:
  A man who's attached goes with his action,
  to that very place to which
  his mind and character cling.
  Reaching the end of his action,
  of whatever he has done in this world—
  From that world he returns
  back to this world,
  back to action.
  "That is the course of a man who desires.</p>
</blockquote>

<p>A different translation is given in wikipedia, but the essence is similar.</p>

<p><a href="https://en.m.wikipedia.org/wiki/Brihadaranyaka_Upanishad#Karma_theory" rel="nofollow noreferrer">https://en.m.wikipedia.org/wiki/Brihadaranyaka_Upanishad#Karma_theory</a></p>

<blockquote>
  <p>One of the earliest formulation of the Karma doctrine occurs in the Brihadaranyaka Upanishad.[46] For example:</p>
  
  <p><strong>Now as a man is like this or like that,
  according as he acts and according as he behaves, so will he be;
  a man of good acts will become good, a man of bad acts, bad;
  he became pure by pure deeds, bad by bad deeds;</strong></p>
  
  <p>And here they say that a person consists of desires,
  and as is his desire, so is his will;
  and as is his will, so is his deed;
  <strong>and whatever deed he does, that he will reap.</strong></p>
  
  <p>— Brihadaranyaka Upanishad, Hymns 4.4.5-4.4.6[48][49]</p>
</blockquote>

<p>Another instance of the doctrine of karma in the same upanishad - </p>

<p><a href="https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc118304.html" rel="nofollow noreferrer">https://www.wisdomlib.org/hinduism/book/the-brihadaranyaka-upanishad/d/doc118304.html</a></p>

<blockquote>
  <p>....tau hotkramya mantrayāṃcakrāte; tau ha yadūcatuḥ <strong>karma</strong> haiva tadūcatuḥ, atha yatpraśaśaṃsatuḥ <strong>karma</strong> haiva tat praśaśaṃsatuḥ; puṇyo vai puṇyena <strong>karmaṇā</strong> bhavati, pāpaḥ pāpeneti | tato ha jāratkārava ārtabhāga upararāma || 13 ||</p>
</blockquote>

<p>Patrick Olivelle's translation - </p>

<blockquote>
  <p>So they left and talked about it. And what did they talk about?—<strong>they talked about nothing but action.</strong> And what did they praise?—<strong>they praised nothing but action. Yajnavalkya told him: "A man turns into something good by good action and into something bad by bad action."</strong></p>
</blockquote>

<p>It has been shown above that two of the cardinal doctrines of buddhism - karma and reincarnation - are already present in the pre-Buddhistic upanishads. </p>

<p>PS: This can become a long post, so I will either write a separate answer for other points or will extend this later.</p>
 471: <p>What was before the Buddha? The Vedas and the earliest Upanishads (Brhadaranyaka, Chandogya) came before the Buddha.</p>

<p>A few other Upanishads (Taittiriya, Aitareya, and Kausitaki) and the Nyaya school of logic may have developed around the same time as the Buddha.</p>

<p>If you look at the scholarly dates given in Wikipedia, all Vedanta schools, Samkhya, Yogasutras of Patanjali, Purva Mimamsa school, the rest of the Upanishads (Kena, Katha, Isa, Svetasvatara, Mundaka, Prasna, Mandukya), Brahmasutras and Bhagavad Gita all came after the Buddha's time.</p>

<p>The closest Hindu school of philosophy to Buddhism, appears to be Advaita Vedanta. Gaudapada and Adi Shankara who founded Advaita Vedanta lived around 6th to 7th century CE. The Buddha lived over a thousand years earlier.</p>

<p>I imagined that Advaita Vedanta influenced Indian Mahayana schools, but it turns out that it may be the other way round. Nagarjuna, the founder of the Madhyamaka school, lived around 150 - 250 CE. Asanga and Vasubandhu, the founders of the Yogacara school, lived around 3rd to 4th century CE.</p>

<p>All this info can be found in Wikipedia.</p>

<p><strong>So, who copied who?</strong></p>

<hr>

<p>The Buddha certainly used terms like karma and dharma from the culture around him, but he redefined those terms based on his teachings.</p>

<p>Let me give you an example. The term "karma" (which simply means action) originates from the Brhadaranyaka Upanishad that predates the Buddha by at least a century. It introduces the idea that doing good makes you good and brings good results, and vice versa.</p>

<p>Later, the Bhagavad Gita (in chapters 2 and 3), which comes 2 centuries after the Buddha, says that the dharma (here meaning duty) of a warrior is to fight for a just cause. If a warrior fights and kills another, while performing his duty, but does so as a sacrifice or offering to God, without any kind of attachment, including to the fruits of action, then the warrior will be freed from sin. On the other hand, if he shirks his responsibility and duty, he would incur sin. This is called karma yoga, which is the title of chapter 3.</p>

<p>On the other hand, in Buddhism, karma is always related to an individual's intention which starts as a thought but is later manifested and exerted through thoughts and actions. The intention is the most important thing. </p>

<p>From the <a href="https://www.accesstoinsight.org/tipitaka/an/an06/an06.063.than.html" rel="nofollow noreferrer">AN 6.63</a>:</p>

<blockquote>
  <p>"Intention, I tell you, is kamma. Intending, one does kamma by way of
  body, speech, &amp; intellect."</p>
</blockquote>

<p>In <a href="https://www.accesstoinsight.org/tipitaka/sn/sn42/sn42.003.than.html" rel="nofollow noreferrer">SN 42.3</a>, a warrior asks the Buddha whether he would go to heavan if he dies in battle. The Buddha states that he would instead be reborn in hell because of exerting the intention to violently kill another human being. It's all about the mind. Please also see <a href="https://buddhism.stackexchange.com/a/34589/471">this answer</a>. Killing because of duty violates the first precept. Pure self-defense may be acceptable for lay people, though.</p>

<p>The term dharma could mean righteousness, duty, order, religion in Hindu texts. In Buddhism, the term dharma or dhamma could mean teachings, phenomena, complex mental concepts. It's slightly different, but related.</p>

<p>With these examples it should be clear that although Hinduism and Buddhism share the terms karma and dharma, they are actually not quite the same.</p>

<hr>

<p>One thing is clear. Anatta or Anatman is uniquely Buddhist, and it clearly separates all Hindu philosophy from Buddhism. There can be no Vedanta without Atman, and there can be no Buddhism without Anatman.</p>
 8157: <p>'<a href="https://en.wikipedia.org/wiki/Hinduism" rel="nofollow noreferrer">Hinduism</a>' did not exist when the Buddha was alive, as follows from Wikipedia:</p>

<blockquote>
  <p>This "Hindu synthesis" started to develop between 500 BCE and 300
  CE, after the end of the Vedic period (1500 to 500 BCE), and
  flourished in the medieval period, with the decline of Buddhism in
  India</p>
  
  <p><a href="https://en.wikipedia.org/wiki/Hinduism" rel="nofollow noreferrer">Wkipedia: Hinduism</a></p>
</blockquote>

<p>When Buddha was alive, the religion of the Brahmin priests we call 'Brahmanism', which was far more limited in scope than Hinduism, per the stock description from the Pali suttas below:</p>

<blockquote>
  <p>Now at that time the brahmin...had mastered the <strong>Three Vedas</strong>, together
  with their vocabularies, ritual, phonology and etymology and the
  testament as fifth. He knew philology and grammar, and was well versed
  in cosmology and the marks of a great man.</p>
  
  <p><a href="https://suttacentral.net/mn91/en/sujato" rel="nofollow noreferrer">MN 91</a></p>
</blockquote>

<p>The Three Vedas are explained in Wikipedia as follows:</p>

<blockquote>
  <p>The canonical division of the Vedas is fourfold (turīya) viz.,</p>
  
  <ol>
  <li><p>Rigveda (RV)</p></li>
  <li><p>Yajurveda (YV, with the main division TS vs. VS) </p></li>
  <li><p>Samaveda (SV)</p></li>
  <li><p>Atharvaveda (AV)</p></li>
  </ol>
  
  <p>Of these, the <strong>first three were the principal original division, also
  called "trayī vidyā"; that is, "the triple science"</strong> of <strong>reciting hymns
  (Rigveda), performing sacrifices (Yajurveda) and chanting songs
  (Samaveda)</strong>. The Rigveda is the oldest work, which Witzel
  states are probably from the period of 1900 to 1100 BCE. Witzel, also
  notes that it is the Vedic period itself, where incipient lists divide
  the Vedic texts into three (trayī) or four branches: Rig, Yajur, Sama
  and Atharva</p>
  
  <p><a href="https://en.wikipedia.org/wiki/Vedas#Four_Vedas" rel="nofollow noreferrer">Wiki</a></p>
</blockquote>

<p>If you read the <a href="https://suttacentral.net/mn-brahmanavagga" rel="nofollow noreferrer">Brāhmaṇa Vagga in the Majjhima Nikaya</a>, there was no Hinduism. In fact, Hinduism, as inferred by Wikipedia (in the 1st quote above), probably copied from Buddhism. </p>

<p>For example (while I am happy to be corrected), I do not recall reading in the Pali suttas any detailed discussion/debate between the Brahmins &amp; the Buddha about respective theories/doctrines of karma &amp; reincarnation. In the little I researched, I found no systematic doctrine of karma &amp; reincarnation in the Three Vedas. Even when I browsed some later '<a href="https://en.wikipedia.org/wiki/Upanishads" rel="nofollow noreferrer">Upanishads</a>', I found no mature systematic doctrine about karma &amp; reincarnation (apart from the ideas of one certain individual philosopher). </p>

<p>Again, if we read the <a href="https://suttacentral.net/mn-brahmanavagga" rel="nofollow noreferrer">Brāhmaṇa Vagga in the Majjhima Nikaya</a>, we find the Brahmins were similar to the Hebrews (and probably many other tribal groups), where their belief system was about how they were '<em>God's chosen people</em>' or '<em>born from Brahma's mouth/breath</em>' (while the other castes were born from lesser parts of Brahma's body).</p>

<p>Some useful links from Sutta Central, with lots of links, books &amp; research, are:</p>

<ul>
<li><p><a href="https://discourse.suttacentral.net/t/the-early-upanishads-a-nice-introduction-to-the-pre-buddhist-tradition/3566" rel="nofollow noreferrer">The early Upanishads: a nice introduction to the pre-Buddhist tradition</a></p></li>
<li><p><a href="https://discourse.suttacentral.net/t/rebirth-reincarnation-in-the-brahman-vedas/5571/22" rel="nofollow noreferrer">Rebirth &amp; reincarnation in the Brahman Vedas</a></p></li>
</ul>

<p>Note: While the Pali suttas never mention the 'Upanishads', the reincarnation orientated leader of Sutta Central, namely, Bhikkhu Sujato, appears intent to follow conventional historians rather than follow the Pali suttas, in his efforts to back-date the Upanishads to prior to Buddhism. If we place our trust in the Pali suttas, we find what existed prior to the Buddha was the Three Vedas &amp; their accompaniments. </p>

<p>An answer about this topic by Bhikkhu Yuttadhammo is here: <a href="https://buddhism.stackexchange.com/questions/8323/did-the-buddha-ever-mention-the-upanishads-or-the-vedas">Did the Buddha ever mention the Upanishads or the Vedas?</a></p>

<p>Lastly, if you wish to be a real Buddhist, it is not possible to believe the Buddha copied any of his core teachings from Brahmanism/Hinduism because the suttas say what the Buddha taught he "<em>never heard before</em>". "A Buddha" cannot copy other doctrines otherwise he/she cannot be called "<em>A Perfectly Self-Enlightened Buddha</em>" ("<a href="https://suttacentral.net/define/samm%C4%81sambuddha" rel="nofollow noreferrer"><em>Sammasambuddha</em></a>"). </p>

<blockquote>
  <p>'Arising, arising!' — At this thought, monks, there arose in me,
  concerning things unheard of before, vision, knowledge, understanding,
  light.</p>
  
  <p>'Cessation, cessation!' — At this thought, monks, there arose in me,
  concerning things unheard of before, vision, knowledge, understanding,
  light."</p>
  
  <p><a href="https://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.010.wlsh.html" rel="nofollow noreferrer">SN 12.10</a></p>
  
  <hr>
  
  <p>Vision arose, insight arose, discernment arose, knowledge arose, illumination arose within me with regard to things never heard before:</p>
  
  <p><a href="https://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.011.than.html" rel="nofollow noreferrer">Dhammacakkappavattana Sutta</a></p>
</blockquote>
