user254: Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?
I guess that "perceptions" and "feelings" are perhaps dependent on sensual contact. Is there anything else they're dependent on?
Are "form" and "consciousness" dependently originated, and what (conditions or causes) do they depend on?
Does "eye consciousness" exist when there's no contact? In a blind person, for example?
If all five aggregates are indeed saṅkhāras, then what is the aggregate called "formation" (saṅkhāra)? What is the difference in the meaning in the word "saṅkhāra" when it's used to identify that one aggregate, as opposed to when it's used to characterise all aggregates?
Is it right to call e.g. the doctrine of the "four noble truths" a dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not subject to decay ... or is this a theory about Dhamma (i.e. a meta-dhamma) proposed by some schools and not others? Is awareness of (e.g. perception of) the dhamma a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent?

user8157: The word "saṅkhāra" has many meanings, such as:

"Compounded things formed by causes & conditions" 
Mental aggregate of thinking & creating (sankhara khandha) 
"Mental proliferating of thought". 
Etc; etc; etc. 

This old blog may help; although I need to re-read it for accuracy. 
Therefore, as "compounded things" (meaning #1), each of the five aggregates are saṅkhāras, as follows:

Rūpaṃ kho āvuso channa, aniccaṃ, vedanā aniccā, saññā aniccā, saṃkhārā aniccā, viññāṇaṃ aniccaṃ, rūpaṃ anantā, vedanā anattā, saññā
  anattā, saṃkhārā anattā, viññāṇaṃ anattā, sabbe saṃkhārā aniccā, sabbe
  dhammā anattā
Form, friend Channa, is impermanent. Feeling is impermanent. Perception is impermanent. Mental formations (saṃkhārā) are
  impermanent. Consciousness is impermanent. Form is not-self. Feeling
  is not-self. Perception is not-self. Mental formations are not-self.
  Consciousness is not-self. All (sabbe) conditioned things (saṃkhārā)
  are impermanent (aniccā). All (sabbe) phenomena (dhammā) are not-self
  (anattā).
SN 22.90

Being compounded things, they must be impermanent and originated from causes (idappaccayatā). 
It is important to distinguish between idappaccayatā and paticcasamuppada; otherwise we will fall into Mahayana by using the term "dependently originated" inaccurately.  
Paticcasamuppada is about how ignorance manifests over 12 conditions to cause sorrow, lamentation, pain, grief & despair and the whole mass of suffering. 
Idappaccayatā is the general principle of cause & effect. Therefore, a physical eye, for example, is formed via idappaccayatā because it is made from atoms, neurons, skins, etc. Merely for the physical scientific reasons a physical eye is made up of different physical parts is why it is a sankhara. The interaction of the mind is not necessarily for the physical eye to be a sankhara. 
Again, the more we fall under Mara's spell of Phenomenology; the more we spin around and around in questions.  The spell of Mara is like this; dragging into samsara.

user471: If all five aggregates are indeed saṅkhāras, then what is the aggregate called "formation" (saṅkhāra)?
Please read this answer for more info on sankharas based on Bhikkhu Bodhi's essay "Anicca Vata Sankhara". I quote the TL;DR version from that answer:

Sankharas are "co-doings," things that act in concert with other
  things, or things that are made by a combination of other things. Ven.
  Bodhi uses "formations" or "volitional formations" as his preferred
  translation.
There are 3 uses of the term Sankhara in the scriptures:

Second link in dependent origination - when ignorance and craving underlie our stream of consciousness, our volitional actions
  of body, speech, and mind become forces with the capacity to produce
  results, including "rebirth".
The fourth of the five aggregates - volition regarding forms, sounds, smells, tastes, tactile objects, and ideas. Also covers all
  factors of mind except feeling and perception.
All conditioned and compounded things including mountains, fields, and forests; towns and cities; food and drink; jewelry, cars, and
  computers.

The only thing which is unconditioned and uncompounded is Nibbana.

Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?
Yes, in all the different meanings of sankhara, they are always impermanent and conditioned (depend on other things for their arising and ceasing).
Are "form" and "consciousness" dependently originated, and what (conditions or causes) do they depend on?
MN 148 explains the arising of consciousness:

"Dependent on the eye & forms there
  arises consciousness at the eye. Dependent on the ear & sounds there
  arises consciousness at the ear. Dependent on the nose & aromas there
  arises consciousness at the nose. Dependent on the tongue & flavors
  there arises consciousness at the tongue. Dependent on the body &
  tactile sensations there arises consciousness at the body. Dependent
  on the intellect & ideas there arises consciousness at the intellect.
  'The six classes of consciousness should be known.'

Meanwhile, form as one of the five aggregates refers to body, and it being conditioned and compounded is explained in MN 74:

Now, Aggivessana, this body — endowed with form, composed of the four
  primary elements, born from mother & father, nourished with rice &
  porridge, subject to inconstancy, rubbing, pressing, dissolution, and
  dispersion — should be envisioned as inconstant, stressful, a disease,
  a cancer, an arrow, painful, an affliction, alien, a disintegration,
  an emptiness, not-self.

Does "eye consciousness" exist when there's no contact? In a blind person, for example?
According to SN 12.44:

Dependent on the eye & forms there arises eye-consciousness. The
  meeting of the three is contact. From contact as a requisite condition
  comes feeling.

"Contact" in this quote refers to mental contact and not physical contact. When there is physical contact between eye and forms (in this context, "form" means visual objects), eye-consciousness arises. The meeting of the three would result in mental contact.
This is only my speculation, but presumably, a blind person can see darkness or black.
Is it right to call e.g. the doctrine of the "four noble truths" a dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not subject to decay
According to AN 3.134, the Dhamma does not depend on the coming of a Buddha:

"Monks, whether or not there is the arising of Tathagatas, this
  property stands — this steadfastness of the Dhamma, this orderliness
  of the Dhamma: All processes are inconstant. ... All processes are
  stressful. ... All phenomena are not-self.

According to this essay by Ajahn Sumedo:

Akalikadhamma means that Dhamma is not bound by any time condition.
  The word akala means timeless. Our conceptual mind can’t conceive of
  anything that is timeless, because our conceptions and perceptions are
  time-based conditions, but what we can say is that Dhamma is akala,
  not bound by time.

Is awareness of (e.g. perception of) the dhamma a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent?
While the Dhamma (teachings) may not be sankhara, the mental concepts built around it definitely is sankhara, which is why seeing it through wisdom (through vipassana) is needed, as compared to intellectualizing it.

user-1: 
Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?

Yes, all khanda are saṅkhāra. They are all impermanent and dependently originated.

I guess that "perceptions" and "feelings" are perhaps dependent on
  sensual contact. Is there anything else they're dependent on?

They are also dependent on objects and citta (if memory serves). Check out the Abhidhamma, and in particular the Dependent Origination chapter and the Patthana.

Are "form" and "consciousness" dependently originated, and what
  (conditions or causes) do they depend on?

Yes, of course. They too are dependently originated. Form has 4 causes: kamma, temperature, nutriment and consciousness.
Consciousness can be caused by objects, Nibbana being the object for supra mundane consciousness and ordinary sense objects for the senses. Kamma can be a cause for all resultant types of consciousnesses. I would refer, again, to the Abhidhamma for further clarification.

Does "eye consciousness" exist when there's no contact? In a blind
  person, for example?

No, eye consciousness arises with an visible object. Light has to be there and attention. When the object ceases so does the accompanying eye consciousness. For instance, when one is in deep sleep, at those moments there is no eye consciousness, seeing doesn't take place. (Again, this is from an Abhidhamma point of view.)

If all five aggregates are indeed saṅkhāras, then what is the
  aggregate called "formation" (saṅkhāra)? What is the difference in the
  meaning in the word "saṅkhāra" when it's used to identify that one
  aggregate, as opposed to when it's used to characterise all
  aggregates?

Saṅkhāra khanda would, f.i., simply be thinking. Except for feeling and perception all other 50 mental factors are part of the Saṅkhāra khanda. That includes kamma, attention, contact, metta, karuna, and so forth.
The difference depends, imho, on the context in which the term is used, the form of classification used.

Is it right to call e.g. the doctrine of the "four noble truths" a
  dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not
  subject to decay ... or is this a theory about Dhamma (i.e. a
  meta-dhamma) proposed by some schools and not others? 

Depends what you mean here with Dhamma. Dhamma in the sense of doctrine: yes, that too will disappear, at least according to the Buddha. When you mean Dhamma in the sense of nature or natural law: then no, nature will always be nature. The way the law of nature works can be forgotten, of course. Till the next Buddha shows up and investigates and sees the truth and law of nature again.

Is awareness of
  (e.g. perception of) the dhamma a saṅkhāra, which depends on contact
  (e.g. contact between mind-object and mind-consciousness), and
  impermanent?

Yes, it is.

user43: -- "Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?"
In my understanding, it's the experience of "my life" that is a saṅkhāra - while the five aggregates (lit. "heaps") are called that because they are an analytical classification of the experience into functional groups, they do not exist as anything separate to begin with:

The Elder said: ‘A hard thing has the Blessed done, great king.’
‘Which hard thing has the Blessed done, venerable Nagasena?’
‘The hard thing the Blessed has done, great king, is the analysis of all the formless dhammas - of the mind and everything related to mind - that unfold on the same foundation: here is Phassa/Contact, here is Vedana/Feeling, here is Sanna/Recognition, here is Cetana/Intention, here is Citta/Thought.
‘Give me an example.’
‘For example, great king, someone were to sail out to the open sea, and taking some water in the palm of his hand, were to taste it. Would he be able to tell: here is water that came from the Ganges, here is from Jumna, here is from Aciravatī, here is from Sarabhū, here is from Mahī?’
‘That would be difficult to do, venerable.’
‘That which the Blessed has done, is even more difficult, great king - the analysis of all the formless dhammas - of the mind and everything related to mind - that unfold on the same foundation: here is Phassa/Contact, here is Vedana/Feeling, here is Sanna/Recognition, here is Cetana/Intention, here is Citta/Thought’

The ocean metaphor used by Nagasena in Milindapanha serves to illustrate that our normal experience is completely unified, just like the water in the ocean is an indistinguishable blend of waters from multiple rivers. Separation of the fire of experience into the five heaps of fuel is an analytical exercise. The heaps themselves do not really exist as something distinct from each other. 
-- "...I guess that "perceptions" and "feelings" are perhaps dependent on sensual contact. Is there anything else they're dependent on? Are "form" and "consciousness" dependently originated, and what (conditions or causes) do they depend on?..."
Yeah, of course they are all impermanent and dependently originated. In fact in one of the suttas Buddha talks about this at length, pointing out how each of the five heaps is not reliable because it depends on some fluctuations outside of one's control. And yes, that included consciousness which depends on external stimuli (here, "rupa").
-- "Does "eye consciousness" exist when there's no contact? In a blind person, for example?"
As @ruben2020 correctly said, it is Contact that depends on consciousness, not the other way around. This is because Contact is phenomenological contact, the experience of coming into contact with an object of sense.
And yet, as you correctly intuited, consciousness is not something that abides - it is an emergent phenomenon that is ephemeral and discontinuous. Continuity and integrity of consciousness(-es) of individual senses, experienced as one seamless whole is a convenient illusion. IMO consciousness is not a good translation for vijnana for exactly this reason - because it implies that it is something abiding that cognizes stuff. Instead, consciousness is ephemeral representation of a stimulus in the mind based on the stimulus relationship with sankharas - imprints left by the previous experiences.
-- "If all five aggregates are indeed saṅkhāras, then what is the aggregate called "formation" (saṅkhāra)? What is the difference in the meaning in the word "saṅkhāra" when it's used to identify that one aggregate, as opposed to when it's used to characterise all aggregates"
The sankhara which is one of the five heaps is called so because it represents aggregation/accumulation of experiences over time, leaving imprints or memories, these imprints then acting as latent tendencies determining person's impulses and reactions. In both cases the word sankhara (lit. "together-made") means something that is constructed or assembled from multiple elements.
-- "Is it right to call e.g. the doctrine of the "four noble truths" a dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not subject to decay ... or is this a theory about Dhamma (i.e. a meta-dhamma) proposed by some schools and not others?"
The Teaching is called Dharma because it expounds the universal law. Indeed, in Chinese Buddhism the word for Dharma is usually translated as "The Law" or "The Rule". That said, in Mahayana Buddhism the fact that even The Teaching itself is conditioned and relative is universally recognized. 
-- "Is awareness of (e.g. perception of) the dhamma a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent?"
My teacher said that "Enlightenment is only a phenomenon, too" - so here you go, this piece is also "a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent".

254: <p>Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?</p>

<p>I guess that "perceptions" and "feelings" are perhaps dependent on sensual contact. Is there anything else they're dependent on?</p>

<p>Are "form" and "consciousness" dependently originated, and what (conditions or causes) do they depend on?</p>

<p>Does "eye consciousness" exist when there's no contact? In a blind person, for example?</p>

<p>If all five aggregates are indeed saṅkhāras, then what is the aggregate called "formation" (saṅkhāra)? What is the difference in the meaning in the word "saṅkhāra" when it's used to identify that one aggregate, as opposed to when it's used to characterise all aggregates?</p>

<p>Is it right to call e.g. the doctrine of the "four noble truths" a dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not subject to decay ... or is this a theory about Dhamma (i.e. a meta-dhamma) proposed by some schools and not others? Is awareness of (e.g. perception of) the dhamma a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent?</p>
 8157: <p>The word "saṅkhāra" has many meanings, such as:</p>

<ol>
<li><p>"Compounded things formed by causes &amp; conditions" </p></li>
<li><p>Mental aggregate of thinking &amp; creating (sankhara khandha) </p></li>
<li><p>"Mental proliferating of thought". </p></li>
<li><p>Etc; etc; etc. </p></li>
</ol>

<p>This <a href="https://dhammadhatu.wordpress.com/2016/06/13/the-word-sankhara-in-context/" rel="nofollow noreferrer">old blog</a> may help; although I need to re-read it for accuracy. </p>

<p>Therefore, as "compounded things" (meaning #1), each of the five aggregates are saṅkhāras, as follows:</p>

<blockquote>
  <p><em>Rūpaṃ kho āvuso channa, aniccaṃ, vedanā aniccā, saññā aniccā, saṃkhārā aniccā, viññāṇaṃ aniccaṃ, rūpaṃ anantā, vedanā anattā, saññā
  anattā, saṃkhārā anattā, viññāṇaṃ anattā, sabbe saṃkhārā aniccā, sabbe
  dhammā anattā</em></p>
  
  <p><em>Form, friend Channa, is impermanent. Feeling is impermanent. Perception is impermanent. Mental formations (saṃkhārā) are
  impermanent. Consciousness is impermanent. Form is not-self. Feeling
  is not-self. Perception is not-self. Mental formations are not-self.
  Consciousness is not-self. <strong>All (sabbe) conditioned things (saṃkhārā)
  are impermanent (aniccā)</strong>. All (sabbe) phenomena (dhammā) are not-self
  (anattā).</em></p>
  
  <p><em>SN 22.90</em></p>
</blockquote>

<p>Being compounded things, they must be impermanent and originated from causes (<em>idappaccayatā</em>). </p>

<p>It is important to distinguish between idappaccayatā and paticcasamuppada; otherwise we will fall into Mahayana by using the term "dependently originated" inaccurately.  </p>

<p>Paticcasamuppada is about how ignorance manifests over 12 conditions to cause sorrow, lamentation, pain, grief &amp; despair and the whole mass of suffering. </p>

<p>Idappaccayatā is the general principle of cause &amp; effect. Therefore, a physical eye, for example, is formed via idappaccayatā because it is made from atoms, neurons, skins, etc. Merely for the physical scientific reasons a physical eye is made up of different physical parts is why it is a sankhara. The interaction of the mind is not necessarily for the physical eye to be a sankhara. </p>

<p>Again, the more we fall under Mara's spell of Phenomenology; the more we spin around and around in questions.  The spell of Mara is like this; dragging into samsara.</p>
 471: <p><em>If all five aggregates are indeed saṅkhāras, then what is the aggregate called "formation" (saṅkhāra)?</em></p>

<p>Please read <a href="https://buddhism.stackexchange.com/a/22530/471">this answer</a> for more info on sankharas based on Bhikkhu Bodhi's essay "<a href="http://www.accesstoinsight.org/lib/authors/bodhi/bps-essay_43.html" rel="nofollow noreferrer">Anicca Vata Sankhara</a>". I quote the TL;DR version from that answer:</p>

<blockquote>
  <p>Sankharas are "co-doings," things that act in concert with other
  things, or things that are made by a combination of other things. Ven.
  Bodhi uses "formations" or "volitional formations" as his preferred
  translation.</p>
  
  <p>There are 3 uses of the term Sankhara in the scriptures:</p>
  
  <ol>
  <li>Second link in dependent origination - when ignorance and craving underlie our stream of consciousness, our volitional actions
  of body, speech, and mind become forces with the capacity to produce
  results, including "rebirth".</li>
  <li>The fourth of the five aggregates - volition regarding forms, sounds, smells, tastes, tactile objects, and ideas. Also covers all
  factors of mind except feeling and perception.</li>
  <li>All conditioned and compounded things including mountains, fields, and forests; towns and cities; food and drink; jewelry, cars, and
  computers.</li>
  </ol>
  
  <p>The only thing which is unconditioned and uncompounded is Nibbana.</p>
</blockquote>

<p><em>Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?</em></p>

<p>Yes, in all the different meanings of sankhara, they are always impermanent and conditioned (depend on other things for their arising and ceasing).</p>

<p><em>Are "form" and "consciousness" dependently originated, and what (conditions or causes) do they depend on?</em></p>

<p><a href="https://www.accesstoinsight.org/tipitaka/mn/mn.148.than.html" rel="nofollow noreferrer">MN 148</a> explains the arising of consciousness:</p>

<blockquote>
  <p>"Dependent on the eye &amp; forms there
  arises consciousness at the eye. Dependent on the ear &amp; sounds there
  arises consciousness at the ear. Dependent on the nose &amp; aromas there
  arises consciousness at the nose. Dependent on the tongue &amp; flavors
  there arises consciousness at the tongue. Dependent on the body &amp;
  tactile sensations there arises consciousness at the body. Dependent
  on the intellect &amp; ideas there arises consciousness at the intellect.
  'The six classes of consciousness should be known.'</p>
</blockquote>

<p>Meanwhile, form as one of the five aggregates refers to body, and it being conditioned and compounded is explained in <a href="https://www.accesstoinsight.org/tipitaka/mn/mn.074.than.html" rel="nofollow noreferrer">MN 74</a>:</p>

<blockquote>
  <p>Now, Aggivessana, <strong>this body — endowed with form, composed of the four
  primary elements, born from mother &amp; father, nourished with rice &amp;
  porridge</strong>, subject to inconstancy, rubbing, pressing, dissolution, and
  dispersion — should be envisioned as inconstant, stressful, a disease,
  a cancer, an arrow, painful, an affliction, alien, a disintegration,
  an emptiness, not-self.</p>
</blockquote>

<p><em>Does "eye consciousness" exist when there's no contact? In a blind person, for example?</em></p>

<p>According to <a href="https://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.044.than.html" rel="nofollow noreferrer">SN 12.44</a>:</p>

<blockquote>
  <p>Dependent on the eye &amp; forms there arises eye-consciousness. The
  meeting of the three is contact. From contact as a requisite condition
  comes feeling.</p>
</blockquote>

<p>"Contact" in this quote refers to mental contact and not physical contact. When there is physical contact between eye and forms (in this context, "form" means visual objects), eye-consciousness arises. The meeting of the three would result in mental contact.</p>

<p>This is only my speculation, but presumably, a blind person can see darkness or black.</p>

<p><em>Is it right to call e.g. the doctrine of the "four noble truths" a dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not subject to decay</em></p>

<p>According to <a href="https://www.accesstoinsight.org/tipitaka/an/an03/an03.134.than.html" rel="nofollow noreferrer">AN 3.134</a>, the Dhamma does not depend on the coming of a Buddha:</p>

<blockquote>
  <p>"Monks, whether or not there is the arising of Tathagatas, this
  property stands — this steadfastness of the Dhamma, this orderliness
  of the Dhamma: All processes are inconstant. ... All processes are
  stressful. ... All phenomena are not-self.</p>
</blockquote>

<p>According to <a href="http://www.buddhanet.net/nowknow1.htm" rel="nofollow noreferrer">this essay</a> by Ajahn Sumedo:</p>

<blockquote>
  <p>Akalikadhamma means that Dhamma is not bound by any time condition.
  The word akala means timeless. Our conceptual mind can’t conceive of
  anything that is timeless, because our conceptions and perceptions are
  time-based conditions, but what we can say is that Dhamma is akala,
  not bound by time.</p>
</blockquote>

<p><em>Is awareness of (e.g. perception of) the dhamma a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent?</em></p>

<p>While the Dhamma (teachings) may not be sankhara, the mental concepts built around it definitely is sankhara, which is why seeing it through wisdom (through vipassana) is needed, as compared to intellectualizing it.</p>
 -1: <blockquote>
  <p>Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?</p>
</blockquote>

<p>Yes, all khanda are saṅkhāra. They are all impermanent and dependently originated.</p>

<blockquote>
  <p>I guess that "perceptions" and "feelings" are perhaps dependent on
  sensual contact. Is there anything else they're dependent on?</p>
</blockquote>

<p>They are also dependent on objects and citta (if memory serves). Check out the Abhidhamma, and in particular the Dependent Origination chapter and the Patthana.</p>

<blockquote>
  <p>Are "form" and "consciousness" dependently originated, and what
  (conditions or causes) do they depend on?</p>
</blockquote>

<p>Yes, of course. They too are dependently originated. Form has 4 causes: kamma, temperature, nutriment and consciousness.
Consciousness can be caused by objects, Nibbana being the object for supra mundane consciousness and ordinary sense objects for the senses. Kamma can be a cause for all resultant types of consciousnesses. I would refer, again, to the Abhidhamma for further clarification.</p>

<blockquote>
  <p>Does "eye consciousness" exist when there's no contact? In a blind
  person, for example?</p>
</blockquote>

<p>No, eye consciousness arises with an visible object. Light has to be there and attention. When the object ceases so does the accompanying eye consciousness. For instance, when one is in deep sleep, at those moments there is no eye consciousness, seeing doesn't take place. (Again, this is from an Abhidhamma point of view.)</p>

<blockquote>
  <p>If all five aggregates are indeed saṅkhāras, then what is the
  aggregate called "formation" (saṅkhāra)? What is the difference in the
  meaning in the word "saṅkhāra" when it's used to identify that one
  aggregate, as opposed to when it's used to characterise all
  aggregates?</p>
</blockquote>

<p>Saṅkhāra khanda would, f.i., simply be thinking. Except for feeling and perception all other 50 mental factors are part of the Saṅkhāra khanda. That includes kamma, attention, contact, metta, karuna, and so forth.
The difference depends, imho, on the context in which the term is used, the form of classification used.</p>

<blockquote>
  <p>Is it right to call e.g. the doctrine of the "four noble truths" a
  dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not
  subject to decay ... or is this a theory about Dhamma (i.e. a
  meta-dhamma) proposed by some schools and not others? </p>
</blockquote>

<p>Depends what you mean here with Dhamma. Dhamma in the sense of doctrine: yes, that too will disappear, at least according to the Buddha. When you mean Dhamma in the sense of nature or natural law: then no, nature will always be nature. The way the law of nature works can be forgotten, of course. Till the next Buddha shows up and investigates and sees the truth and law of nature again.</p>

<blockquote>
  <p>Is awareness of
  (e.g. perception of) the dhamma a saṅkhāra, which depends on contact
  (e.g. contact between mind-object and mind-consciousness), and
  impermanent?</p>
</blockquote>

<p>Yes, it is.</p>
 43: <p>-- "<em>Are the five aggregates all saṅkhāras -- are they impermanent and dependently originated?</em>"</p>

<p>In my understanding, it's <em>the experience</em> of "my life" that is a saṅkhāra - while the five aggregates (lit. "heaps") are called that because they are an analytical classification of the experience into functional groups, they do not exist as anything separate to begin with:</p>

<blockquote>
  <p>The Elder said: ‘A hard thing has the Blessed done, great king.’</p>
  
  <p>‘Which hard thing has the Blessed done, venerable Nagasena?’</p>
  
  <p>‘The hard thing the Blessed has done, great king, is the analysis of all the formless dhammas - of the mind and everything related to mind - that unfold on the same foundation: here is Phassa/Contact, here is Vedana/Feeling, here is Sanna/Recognition, here is Cetana/Intention, here is Citta/Thought.</p>
  
  <p>‘Give me an example.’</p>
  
  <p>‘For example, great king, someone were to sail out to the open sea, and taking some water in the palm of his hand, were to taste it. Would he be able to tell: here is water that came from the Ganges, here is from Jumna, here is from Aciravatī, here is from Sarabhū, here is from Mahī?’</p>
  
  <p>‘That would be difficult to do, venerable.’</p>
  
  <p>‘That which the Blessed has done, is even more difficult, great king - the analysis of all the formless dhammas - of the mind and everything related to mind - that unfold on the same foundation: here is Phassa/Contact, here is Vedana/Feeling, here is Sanna/Recognition, here is Cetana/Intention, here is Citta/Thought’</p>
</blockquote>

<p>The ocean metaphor used by Nagasena in Milindapanha serves to illustrate that our normal experience is completely unified, just like the water in the ocean is an indistinguishable blend of waters from multiple rivers. Separation of the fire of experience into the five heaps of fuel is an analytical exercise. The heaps themselves do not really exist as something distinct from each other. </p>

<p>-- <em>"...I guess that "perceptions" and "feelings" are perhaps dependent on sensual contact. Is there anything else they're dependent on? Are "form" and "consciousness" dependently originated, and what (conditions or causes) do they depend on?..."</em></p>

<p>Yeah, of course they are all impermanent and dependently originated. In fact in one of the suttas Buddha talks about this at length, pointing out how each of the five heaps is not reliable because it depends on some fluctuations outside of one's control. And yes, that included consciousness which depends on external stimuli (here, "rupa").</p>

<p>-- <em>"Does "eye consciousness" exist when there's no contact? In a blind person, for example?"</em></p>

<p>As @ruben2020 correctly said, it is Contact that depends on consciousness, not the other way around. This is because Contact is phenomenological contact, the experience of coming into contact with an object of sense.</p>

<p>And yet, as you correctly intuited, consciousness is not something that abides - it is an emergent phenomenon that is ephemeral and discontinuous. Continuity and integrity of consciousness(-es) of individual senses, experienced as one seamless whole is a convenient illusion. IMO consciousness is not a good translation for vijnana for exactly this reason - because it implies that it is something abiding that cognizes stuff. Instead, consciousness is ephemeral representation of a stimulus in the mind based on the stimulus relationship with sankharas - imprints left by the previous experiences.</p>

<p>-- <em>"If all five aggregates are indeed saṅkhāras, then what is the aggregate called "formation" (saṅkhāra)? What is the difference in the meaning in the word "saṅkhāra" when it's used to identify that one aggregate, as opposed to when it's used to characterise all aggregates"</em></p>

<p>The sankhara which is one of the five heaps is called so because it represents aggregation/accumulation of experiences over time, leaving imprints or memories, these imprints then acting as latent tendencies determining person's impulses and reactions. In both cases the word sankhara (lit. "together-made") means something that is constructed or assembled from multiple elements.</p>

<p>-- <em>"Is it right to call e.g. the doctrine of the "four noble truths" a dhamma instead of a saṅkhāra? Is the doctrine unconditioned and not subject to decay ... or is this a theory about Dhamma (i.e. a meta-dhamma) proposed by some schools and not others?"</em></p>

<p>The Teaching is called Dharma because it expounds the universal law. Indeed, in Chinese Buddhism the word for Dharma is usually translated as "The Law" or "The Rule". That said, in Mahayana Buddhism the fact that even The Teaching itself is conditioned and relative is universally recognized. </p>

<p>-- <em>"Is awareness of (e.g. perception of) the dhamma a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent?"</em></p>

<p>My teacher said that "Enlightenment is only a phenomenon, too" - so here you go, this piece is also <em>"a saṅkhāra, which depends on contact (e.g. contact between mind-object and mind-consciousness), and impermanent"</em>.</p>
