user151: Are the Buddha's words the source of the Pali Canon? What evidence is there of the Pali Canon's origin? What do scholars say? 

user8157: In my opinion, all we can know for certain are words spoken or written down by 'a Buddha' (i.e., an awakened enlightened mind) rather than by 'the Buddha' (i.e. Gotama). The only way we can know this is via personal realisation. 

"Knowing thus and seeing thus, would you say, 'The Contemplative says this. We speak thus in line with the Contemplative's words'?"
"No, lord."
"Is it the case that you speak simply in line with what you have known, seen & understood for yourselves?"
"Yes, lord."
"Good, monks. You have been guided by me in this Dhamma which is to be seen here & now, timeless, inviting verification, pertinent, to be
  realized by the observant for themselves."
Mahatanhasankhaya Sutta

For example, at www.accesstoinsight.org, there are four translations of the Four Noble Truths, each one is different and not one of them accords to any meditative experience or realisation. Therefore, not one of them can be regarded as the words of a Buddha. 

in brief, the five bundles of grasping-fuel are painful - Peter Harvey
in short, suffering is the five categories of clinging objects -
  Ñanamoli Thera
in brief the five aggregates subject to grasping are suffering -
  Piyadassi Thera
In short, the five clinging-aggregates are stressful - Thanissaro
  Bhikkhu

However, the confusing translations above of 'saṃkhittena pañchupādāna'k'khandhā dukkhā' does not mean a Buddha did not speak the words 'saṃkhittena pañc'upādāna'k'khandhā dukkhā', which should simply state: "In summary, attaching to the five aggregates is suffering" or "the five attachments to the five aggregates is suffering" (which emphasizes 'attachment' as suffering or the problem rather than the neutral aggregates). 

user1094: Are the Buddha's words the source of the Pali Canon? What evidence is there of the Pali Canon's origin? What do scholars say?
My answers to the questions are based on known facts. Thus I define the Pali canon as follows:
Sets of the Pāli Canon in English Translation and in Pāli (Tipiṭaka).
My answers to the three questions are as follows.


Are the Buddha's words the source of the Pali Canon?

Indeterminate.
The question is for the 'Pali canon'. The Pali Text Society publishes a Pāli Canon. 
Buddha (the Buddha) is an English word with multiple meanings [Oxford Dictionaries]. It is obviously not in the Pali canon. 
PTS Pāli Canon has over 9000 references to the term "bhagavā". Of the 9000 references, only 60 occur in the Abhidhamma Pitaka. 
The term bhagavā is defined by the following expression:

‘itipi so bhagavā arahaṃ sammāsambuddho vijjācaraṇasampanno sugato lokavidū anuttaro purisadammasārathi satthā devamanussānaṃ buddho bhagavā’ti.

The words attributed to Bhagava in the Sutta and Vinaya Pitakas appear to be the major source for the Pāli Canon.


What evidence is there of the Pali Canon's origin?

According to the Sri Lankan Mahavamsa, the Pali Canon was written down in the reign of King Vattagāmini (Vaṭṭagāmiṇi) (1st century BCE) in Sri Lanka, at the Fourth Buddhist council. Most scholars hold that little if anything was added to the Canon after this [Wikipedia}.


What do scholars say?

Scholars generally agree to the origin of the Pali canon as mentioned above. 

user106: The scholar Hans Wolfgang Schumann in his (german) monography "Der historische Buddha - Leben und Lehre des Gotama" (1995) ("the historical Buddha - life and teaching of Gotama, 2005") gave a paragraph on the characteristics of "Pali" as a language. I'll try to translate it correctly to english from the german version (pg 296):           

"The language which the Rajagaha-council used and in which it canonized
  the Word-Of-the-Buddha, has been "Pali", a higher form of the Maghadi,
  which avoided local terms ("mundartliche Formen") and which had
  enriched its vocabulary with terms of related languages in India.
  "Pali" has been a conversational language, which was only spoken by
  educated people, but understood by the common people. The north-indian
  rulers used it as language for governmental and jurisdictive purposes
  - thus it was also well known to the Raja's son Siddhattha Gotama from his early youth. Also Upali and Ananda were likely able to speak it
  fluently.(...)"

A more involved consideration, which references many authors, can be found in this Was ist Pali topic on Aloys Payer's web site (unfortunately there is no english version of it and I cannot do the translation, but Google Translate can translate it adequately).

user-1: You can find a scholar to support almost any view, but the consensus seems to be that the Pali Canon - the only complete version of the early Canon that has survived to the present day - originated shortly after the passing on (parinibbana) of the Buddha (circa 400 BCE); continued to be collected, edited, and revised at least until the middle of the third century BCE, when it achieved its final Pali form more or less; was written down in the first century BCE; and continued to be copied over the intervening centuries, perhaps with fairly minor changes and, of course, errors of transcription, till it was codified during the Fifth Buddhist Council in 1871 and again in 1954. 
No definitive critical edition of the Pali Canon has been produced in accordance with Western scholarly criteria, though I believe one is in the early stages of development. 
Many scholars consider the first four nikayas - the Digha Nikaya, Majjhima Nikaya, Samyyuta Nikaya, and Anguttara Nikaya - to be the most ancient and essential parts of the Canon, along with the Vinaya perhaps, but nothing in the Pali Canon should be considered to be the literal Buddhavacana ("Word of the Buddha") and all of the suttas of the Pali Canon represent an indiscriminate mixture of early and late textual traditions. 
Some people think that the parables of the Buddha are the most authentic, much as some Biblical scholars think that the parables of Yeshua (Jesus) are the most authentic. 
The shortest interval between the Buddha's death and the earliest date for the codification of the Canon is about 150 years, which would correspond to the year 180 in terms of the development of the Christian scriptural tradition for comparison. This is the age of the early Church fathers and well after the period of the canonical gospels of the New Testament. Thus, the Pali Canon incorporates the Buddha's original teachings subject to at least five (or eight) "generations" (but only two lifetimes) of interpretation, codification, and exegesis, arising out of an historical process that was clearly contentious from the very beginning. 
While Pali linguists can distinguish later from earlier texts to some extent, no one can accurately identify the "original teachings" of the Buddha based on any kind of objective heuristic, and those who pretend to do so are usually pursuing a sectarian agenda. Moreover, the simplistic equation of lateness with wrongness is a grossly naive hermeneutic, comparable to the discredited notion of "authorial intent." 
Per contra, the view of those who maintain that the Pali Canon is actually recent, based on the paucity of early mss., is also untenable, since many Pali texts were translated into fairly early Chinese, Tibetan, and even Sanskrit versions that correspond quite well with the Pali texts. Although each of the early schools had its own canon, they all seemed to share and accept a common collection of suttas that were very similar to each other and to the Pali suttas that we have today in the Pali Canon. 
Another relevant point is that the Pali language is not the language actually spoken by the Buddha, but is a hybrid artificial language developed by the early monastics to preserve the teachings of the Buddha and communicate with each other, which clearly indicates that the Canon originated as a result of cultural and geographical differentiation. Scholars generally consider Pali to be closely related to the language of the Buddha, however. Pali linguists have identified earlier and later meanings of certain Pali words that can be used to "date" the texts that contain them, and to a limited extent elucidate their meaning. 
The Canon also travelled from north-east India to Sri Lanka through successive phases - first, a westward expansion, then moving south and finally into Sri Lanka, during which it presumably picked up cultural influences from western India, south-western India, and Sri Lanka itself. It was also preserved by monastics, so we may assume that it was influenced by this fact as well. 
Finally, every point in this summary will be disputed by someone!

user6994: I encourage you to read the following: Bhikkhu Sujato & Bhikkhu Brahmali. The Authenticity of the Early Buddhist Texts.
In this work, their project is to investigate the question of authencity systematically. In that, the approach is quiet academic and might be to your liking.
Page 7, they state a feature of the early Buddhist texts:

The Buddha’s presence as a living figure in the EBTs is overwhelming
and unmistakable. It stands in stark contrast with all other Buddhist
literature, where the Buddha has faded to legend.


Page 8, they assert that, although they accord with the meaning of Buddha Dharma...
> We are not denying the obvious fact that the texts bear all the marks
> of redaction and editing, and that they have been optimised for the
> oral tradition.

Page 151, they state what we owe to the early Buddhist texts:
> We know when the Buddha lived, where he lived, who he associated with,
> how he lived, and what he taught. We know these things with greater
> certainty than for almost any other historical figure from a
> comparable period. And we know this because of the EBTs. All other
> historical and archaeological information about the period depends on
> the EBTs to make sense.
Their overall conclusion is that although the Pali canon "bears the marks of redaction and editing", the meaning accord with the intent of the Buddha. Bhikkhu Sujato and Bhikkhu Brahmali expose various argument (sorted out by chapters, that all constitute different angles: geographical, historical, and so forth) in order to highlight the proximity between what is written in the Pali canon and what the Buddha [presumably] said.

151: <p>Are the Buddha's words the source of the Pali Canon? What evidence is there of the Pali Canon's origin? What do scholars say? </p>
 8157: <p>In my opinion, all we can know for certain are words spoken or written down by 'a Buddha' (i.e., an awakened enlightened mind) rather than by 'the Buddha' (i.e. Gotama). The only way we can know this is via <em>personal realisation</em>. </p>

<blockquote>
  <p><em>"Knowing thus and seeing thus, would you say, 'The Contemplative says this. We speak thus in line with the Contemplative's words'?</em>"</p>
  
  <p><em>"No, lord."</em></p>
  
  <p><em>"Is it the case that you speak simply in line with what you have known, seen &amp; understood for yourselves?"</em></p>
  
  <p><em>"Yes, lord."</em></p>
  
  <p><em>"Good, monks. You have been guided by me in this Dhamma which is to be seen here &amp; now, timeless, inviting verification, pertinent, to be
  realized by the observant for themselves."</em></p>
  
  <p><em>Mahatanhasankhaya Sutta</em></p>
</blockquote>

<p>For example, at <a href="http://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.011.harv.html" rel="nofollow">www.accesstoinsight.org</a>, there are four translations of the Four Noble Truths, each one is different and not one of them accords to any meditative experience or realisation. Therefore, not one of them can be regarded as the words of a Buddha. </p>

<blockquote>
  <p><em>in brief, the five bundles of grasping-fuel are painful - Peter Harvey</em></p>
  
  <p><em>in short, suffering is the five categories of clinging objects -
  Ñanamoli Thera</em></p>
  
  <p><em>in brief the five aggregates subject to grasping are suffering -
  Piyadassi Thera</em></p>
  
  <p><em>In short, the five clinging-aggregates are stressful - Thanissaro
  Bhikkhu</em></p>
</blockquote>

<p>However, the confusing translations above of '<em>saṃkhittena pañchupādāna'k'khandhā dukkhā</em>' does not mean a Buddha did not speak the words '<em>saṃkhittena pañc'upādāna'k'khandhā dukkhā</em>', which should simply state: "In summary, attaching to the five aggregates is suffering" or "the five attachments to the five aggregates is suffering" (which emphasizes 'attachment' as suffering or the problem rather than the neutral aggregates). </p>
 1094: <p><strong>Are the Buddha's words the source of the Pali Canon? What evidence is there of the Pali Canon's origin? What do scholars say?</strong></p>

<p>My answers to the questions are based on known facts. Thus I define the Pali canon as follows:</p>

<p><a href="http://www.palitext.com/palitext/tipitaka.htm" rel="nofollow">Sets of the Pāli Canon in English Translation and in Pāli (Tipiṭaka)</a>.</p>

<p>My answers to the three questions are as follows.</p>

<hr>

<ol>
<li><strong>Are the Buddha's words the source of the Pali Canon?</strong></li>
</ol>

<p>Indeterminate.</p>

<p>The question is for the 'Pali canon'. The Pali Text Society publishes a Pāli Canon. </p>

<p>Buddha (the Buddha) is an English word with multiple meanings [Oxford Dictionaries]. It is obviously not in the Pali canon. </p>

<p>PTS Pāli Canon has over 9000 references to the term "bhagavā". Of the 9000 references, only 60 occur in the Abhidhamma Pitaka. </p>

<p>The term bhagavā is defined by the following expression:</p>

<blockquote>
  <p>‘itipi so bhagavā arahaṃ sammāsambuddho vijjācaraṇasampanno sugato lokavidū anuttaro purisadammasārathi satthā devamanussānaṃ buddho bhagavā’ti.</p>
</blockquote>

<p>The words attributed to Bhagava in the Sutta and Vinaya Pitakas appear to be the major source for the Pāli Canon.</p>

<hr>

<ol start="2">
<li><strong>What evidence is there of the Pali Canon's origin?</strong></li>
</ol>

<p>According to the Sri Lankan Mahavamsa, the Pali Canon was written down in the reign of King Vattagāmini (Vaṭṭagāmiṇi) (1st century BCE) in Sri Lanka, at the Fourth Buddhist council. Most scholars hold that little if anything was added to the Canon after this [Wikipedia}.</p>

<hr>

<ol start="3">
<li><strong>What do scholars say?</strong></li>
</ol>

<p>Scholars generally agree to the origin of the Pali canon as mentioned above. </p>
 106: <p>The scholar Hans Wolfgang Schumann in his (german) monography "Der historische Buddha - Leben und Lehre des Gotama" (1995) ("<a href="http://www.wisdom-books.com/product/historical-buddha/11199/" rel="nofollow">the historical Buddha - life and teaching of Gotama, 2005</a>") gave a paragraph on the characteristics of "Pali" as a language. I'll try to translate it correctly to english from the german version (pg 296):           </p>

<blockquote>
  <p>"The language which the Rajagaha-council used and in which it canonized
  the Word-Of-the-Buddha, has been "Pali", a higher form of the Maghadi,
  which avoided local terms <em>("mundartliche Formen")</em> and which had
  enriched its vocabulary with terms of related languages in India.
  "Pali" has been a conversational language, which was only spoken by
  educated people, but understood by the common people. The north-indian
  rulers used it as language for governmental and jurisdictive purposes
  - thus it was also well known to the Raja's son Siddhattha Gotama from his early youth. Also Upali and Ananda were likely able to speak it
  fluently.(...)"</p>
</blockquote>

<p>A more involved consideration, which references many authors, can be found in this <a href="http://www.payer.de/pali/pali01.htm#1.3." rel="nofollow">Was ist Pali</a> topic on Aloys Payer's web site (unfortunately there is no english version of it and I cannot do the translation, but Google Translate can translate it adequately).</p>
 -1: <p>You can find a scholar to support almost any view, but the consensus seems to be that the Pali Canon - the only complete version of the early Canon that has survived to the present day - originated shortly after the passing on (parinibbana) of the Buddha (circa 400 BCE); continued to be collected, edited, and revised at least until the middle of the third century BCE, when it achieved its final Pali form more or less; was written down in the first century BCE; and continued to be copied over the intervening centuries, perhaps with fairly minor changes and, of course, errors of transcription, till it was codified during the Fifth Buddhist Council in 1871 and again in 1954. </p>

<p>No definitive critical edition of the Pali Canon has been produced in accordance with Western scholarly criteria, though I believe one is in the early stages of development. </p>

<p>Many scholars consider the first four nikayas - the Digha Nikaya, Majjhima Nikaya, Samyyuta Nikaya, and Anguttara Nikaya - to be the most ancient and essential parts of the Canon, along with the Vinaya perhaps, but nothing in the Pali Canon should be considered to be the literal Buddhavacana ("Word of the Buddha") and all of the suttas of the Pali Canon represent an indiscriminate mixture of early and late textual traditions. </p>

<p>Some people think that the parables of the Buddha are the most authentic, much as some Biblical scholars think that the parables of Yeshua (Jesus) are the most authentic. </p>

<p>The shortest interval between the Buddha's death and the earliest date for the codification of the Canon is about 150 years, which would correspond to the year 180 in terms of the development of the Christian scriptural tradition for comparison. This is the age of the early Church fathers and well after the period of the canonical gospels of the New Testament. Thus, the Pali Canon incorporates the Buddha's original teachings subject to at least five (or eight) "generations" (but only two lifetimes) of interpretation, codification, and exegesis, arising out of an historical process that was clearly contentious from the very beginning. </p>

<p>While Pali linguists can distinguish later from earlier texts to some extent, no one can accurately identify the "original teachings" of the Buddha based on any kind of objective heuristic, and those who pretend to do so are usually pursuing a sectarian agenda. Moreover, the simplistic equation of lateness with wrongness is a grossly naive hermeneutic, comparable to the discredited notion of "authorial intent." </p>

<p>Per contra, the view of those who maintain that the Pali Canon is actually recent, based on the paucity of early mss., is also untenable, since many Pali texts were translated into fairly early Chinese, Tibetan, and even Sanskrit versions that correspond quite well with the Pali texts. Although each of the early schools had its own canon, they all seemed to share and accept a common collection of suttas that were very similar to each other and to the Pali suttas that we have today in the Pali Canon. </p>

<p>Another relevant point is that the Pali language is not the language actually spoken by the Buddha, but is a hybrid artificial language developed by the early monastics to preserve the teachings of the Buddha and communicate with each other, which clearly indicates that the Canon originated as a result of cultural and geographical differentiation. Scholars generally consider Pali to be closely related to the language of the Buddha, however. Pali linguists have identified earlier and later meanings of certain Pali words that can be used to "date" the texts that contain them, and to a limited extent elucidate their meaning. </p>

<p>The Canon also travelled from north-east India to Sri Lanka through successive phases - first, a westward expansion, then moving south and finally into Sri Lanka, during which it presumably picked up cultural influences from western India, south-western India, and Sri Lanka itself. It was also preserved by monastics, so we may assume that it was influenced by this fact as well. </p>

<p>Finally, every point in this summary will be disputed by someone!</p>
 6994: <p>I encourage you to read the following: Bhikkhu Sujato &amp; Bhikkhu Brahmali. <a href="https://ocbs.org/wp-content/uploads/2015/09/authenticity.pdf" rel="nofollow noreferrer"><em>The Authenticity of the Early Buddhist Texts</em></a>.</p>
<p>In this work, their project is to investigate the question of authencity <strong>systematically</strong>. In that, the approach is quiet academic and might be to your liking.</p>
<p>Page 7, they state a feature of the early Buddhist texts:</p>
<blockquote>
<p>The Buddha’s presence as a living figure in the EBTs is overwhelming
and unmistakable. It stands in stark contrast with all other Buddhist
literature, where the Buddha has faded to legend.</p>
</blockquote>
<br>
Page 8, they assert that, although they accord with the meaning of Buddha Dharma...
> We are not denying the obvious fact that the texts bear all the marks
> of redaction and editing, and that they have been optimised for the
> oral tradition.
<br>
Page 151, they state what we owe to the early Buddhist texts:
> We know when the Buddha lived, where he lived, who he associated with,
> how he lived, and what he taught. We know these things with greater
> certainty than for almost any other historical figure from a
> comparable period. And we know this because of the EBTs. All other
> historical and archaeological information about the period depends on
> the EBTs to make sense.
<p>Their overall conclusion is that although the Pali canon &quot;bears the marks of redaction and editing&quot;, the meaning accord with the intent of the Buddha. Bhikkhu Sujato and Bhikkhu Brahmali expose various argument (sorted out by chapters, that all constitute different angles: geographical, historical, and so forth) in order to highlight the proximity between what is written in the Pali canon and what the Buddha [presumably] said.</p>
