user121: I've found this to be an interesting question with highly respected monastics falling on both sides of the answer.

user92: Well, I think there is a reason why the path is eightfold and not sevenfold. The Pāḷi Canon is full of encouragements, made by the Buddha, to practice jhānas. It would be stretching the texts a lot to say it isn't necessary. I wouldn't argue over it though.

‘The sage, the withdrawn chief bull,
  the Buddha who awakened to jhāna,
  the One of Broad Wisdom has found
  the opening amid confinement.’
  -AN 9.42, Confinement (Sambādha-suttaṃ) & SN 2.7, Pañcālacaṇḍa (Pañcālacaṇḍa-suttaṃ) 



'There's no jhāna for one with no discernment,
  no discernment for one
  with no jhāna.
  But one with both jhāna & discernment:
  he's on the
  verge of Unbinding.'
  -Dhp v372


user471: From SN 55.5:

“Sir, the factors of stream-entry are associating with good people,
listening to the true teaching, proper attention, and practicing in
line with the teaching.”
“Sappurisasaṃsevo hi, bhante, sotāpattiyaṅgaṃ, saddhammassavanaṃ sotāpattiyaṅgaṃ, yonisomanasikāro sotāpattiyaṅgaṃ,
dhammānudhammappaṭipatti sotāpattiyaṅgan”ti.

According to the sutta above, proper attention (yonisomanasikāra) is required for stream entry.
It's not possible to achieve proper attention, when one is afflicted with the five hindrances. In order to significantly overcome the five hindrances, one needs to have mastered at least the first jhana. You can find more info in this question.
To quote Ven. Dhammavuddho from that question:

The third condition, this word - yoniso manasikara, which I translate
as focused attention. Sometimes they say careful attention. This word
means that when you listen to the Dhamma, you are focused on listening
to the Dhamma. In other words, at that time, you don't have the five
hindrances. If that is so, then you can understand the Dhamma and
attain stream entry.
So who are the people who do not have the five hindrances? In the
suttas, it is stated by the Buddha that as long as a person has not
attained piti and sukha which are secluded from unwholesome states,
which are secluded from sensual pleasures, the five hindrances will
obsess him and obsess him habitually.
... When a person has attained the first jhana, he has eliminated the
five hindrances and the Buddha says that the five hindrances no longer
obsess that person habitually.
So there are two conditions if a person has the hindrances. Firstly,
it obsesses your mind, it enslaves your mind. Secondly, it is
habitual, it is very often there. ... When a person attains the first
jhana, these hindrances reduce to a very low level. ...

In that question, Ven. Dhammavuddho claimed that instead of the first jhana, it is also possible that persons of high IQ can also achieve proper attention, although this is his personal opinion.
From this page on Nirodha Samapatti:

According to Vis.M. XXIII, the entering into this state takes place in
the following way: by means of mental tranquillity (samatha) and
insight (vipassanā) one has to pass through all the 8 absorptions one
after the other up to the sphere of
neither-perception-nor-non-perception and then one has to bring this
state to an end. If, namely, according to the Vis.M., the disciple
(Anāgāmī or Arahat) passes through the absorption merely by means of
tranquillity, i.e. concentration, he will only attain the sphere of
neither-perception-nor-non-perception, and then come to a standstill;
if, on the other hand, he proceeds only with insight, he will reach
the fruition (phala) of Anāgāmī or Arahantship. He, however, who by
means of both faculties has risen from absorption to absorption and,
having made the necessary preparations, brings the sphere of
neither-perception-nor-non-perception to an end, such a one reaches
the state of extinction.

So, according to the Visuddhimagga, the 8 jhanas and Nirodha Samapatti are not absolutely required for attainment of the fruition of anagami and arahat.

user10100: Upacara&Appana Jhana are required for TanhaCarita according to Netti, Kayagatasatisutta's &Mahasatipatthanasutta's  structure, Visuddhimagga DitthivisuddhiNiddesa.
Netti (my english is terrible, so please find the translation yourself):

[81] tattha diṭṭhicarito asmiṃ sāsane pabbajito sallekhānusantatavutti bhavati sallekhe tibbagāravo. taṇhācarito asmiṃ sāsane pabbajito sikkhānusantatavutti bhavati sikkhāya tibbagāravo. diṭṭhicarito sammattaniyāmaṃ okkamanto dhammānusārī bhavati. taṇhācarito sammattaniyāmaṃ okkamanto saddhānusārī bhavati, diṭṭhicarito sukhāya paṭipadāya dandhābhiññāya khippābhiññāya ca niyyāti. taṇhācarito dukkhāya paṭipadāya dandhābhiññāya khippābhiññāya ca niyyāti.
tattha kiṃkāraṇaṃ, yaṃ taṇhācarito dukkhāya paṭipadāya dandhābhiññāya khippābhiññāya ca niyyāti, tassa hi kāmā apariccattā bhavanti, so kāmehi viveciyamāno dukkhena paṭinissarati dandhañca dhammaṃ ājānāti? yo panāyaṃ diṭṭhicarito ayaṃ āditoyeva kāmehi anatthiko bhavati. so tato viveciyamāno khippañca paṭinissarati, khippañca dhammaṃ ājānāti. dukkhāpi paṭipadā duvidhā dandhābhiññā ca khippābhiññā ca. sukhāpi paṭipadā duvidhā dandhābhiññā ca khippābhiññā ca. sattāpi duvidhā mudindriyāpi tikkhindriyāpi. ye mudindriyā, te dandhañca paṭinissaranti dandhañca dhammaṃ ājānanti. ye tikkhindriyā, te khippañca paṭinissaranti, khippañca dhammaṃ ājānanti, imā catasso paṭipadā. ye hi keci niyyiṃsu vā niyyanti vā niyyissanti vā, te imāhi eva catūhi paṭipadāhi. evaṃ ariyā catukkamaggaṃ paññāpenti abudhajanasevitāya bālakantāya rattavāsiniyā nandiyā bhavataṇhāya avaṭṭanatthaṃ [āvaṭṭanatthaṃ (sī. ka.)]. ayaṃ vuccati nandiyāvaṭṭassa nayassa bhūmīti, tenāha ‘‘taṇhañca avijjampi ca samathenā’’ti.

In DesanaHara, TanhaCarita should practice 4 Satipatthana and 4 Jhana. That is compatible with KayagatasatiSutta's commentary which separate Kayanupassana into 2 parts, Samatha and Vipassana.
The structure of KayagatasatiSutta is Samatha, and MahasatipattahanaSutta is Vipassana. This is compatible with many points of MahasatipattahanaSutta's commentary.
That's why in Visuddhimagga DitthivisuddhiNiddesa:

and the purification of consciousness, namely, the eight attainments (Upacara Jhana) together with access concentration (Appana Jhana), has also been dealt with in detail in all its aspects in the Description of Concentration, (Chs. III to XIII) stated under the heading of “consciousness”


Don't combine and don't separate samatha-jhāna, vipassana-jhana,  and lokuttara-jhana without deep understand in the pali canon.
Samatha-jhāna and vipassana-jhana are friends who fight together to win, become Lokuttara-Jhana, together.
Balava Vipassana-Jhana can't grow up with 5 hindrances. Samatha-jhāna can't  attain Nibbana without Understanding in the reality and 7 Anusaya. They are colleagues in the noble eightfold path.
Lokuttara-appana-jhana are them who graduated as a team, maggacittupada (a noble eightfold path; it is not many. It is only one team; it is "ariyo atthangiko Maggo", not "ariya atthangika magga").

user18: Actually, a point that is not well understood is that, among those who follow the Pali canon, there is no controversy over whether some jhāna is necessary; the answer is in all cases yes. The controversy is really over which jhāna is necessary.
There are three types of jhāna in total:

samatha-jhāna - jhāna based on a conceptual object that, due to its conceptual nature, cannot lead to the realization of the nature of reality.

For example, in the Visuddhimagga:

The colour should not be reviewed. The characteristic should not be
  given attention. But rather, while not ignoring the colour, attention
  should be given by setting the mind on the [name] concept as the most
  outstanding mental datum, relegating the colour to the position of a
  property of its physical support. That [conceptual state] can be
  called by anyone he likes among the names for earth (pathavī) such as
  “earth” (pathavī), “the Great One” (mahī), “the Friendly One”
  (medinī), “ground” (bhūmi), “the Provider of Wealth” (vasudhā), “the
  Bearer of Wealth” (vasudharā), etc., whichever suits his manner of
  perception. Still “earth” is also a name that is obvious, so it can be
  developed with the obvious one by saying “earth, earth.” It should be
  adverted to now with eyes open, now with eyes shut. And he should go
  on developing it in this way a hundred times, a thousand times, and
  even more than that, until the learning sign arises.
Path of Purification, IV.29

2. vipassana-jhāna - jhāna based on ultimate reality that allows one to see the three characteristics and thus attain nibbana. As the Mahasi Sayadaw states:

The tranquillity that occurs while one contemplates various phenomena is called momentary concentration, the concentration that lasts momentarily during contemplation. No insight is possible without this momentary concentration. The meditator who has no basic [samatha] jhānic experience and relies on insight meditation alone develops insight through momentary concentration and attains the noble path. This concentration for insight is not confined to a single object. The meditator practising it notes all the mental and physical phenomena that arise. However, at the moment of noting, his mind is fixed on the object and free from distraction. This is obvious to the meditator who practises effectively.
http://www.aimwell.org/sallekha.html

3. lokuttara-jhāna - jhāna that takes a supermundane object (nibbana), and is equivalent to attaining the noble path and fruition. According to Bhante Gunaratana:

But the four jhanas again reappear in a later stage in the development of the path, in direct association with liberating wisdom, and they are then designated the supramundane (lokuttara) jhanas. These supramundane jhanas are the levels of concentration pertaining to the four degrees of enlightenment experience called the supramundane paths (magga) and the stages of liberation resulting form them, the four fruits (phala).
http://www.budsas.org/ebud/jhanas/jhanas01.htm

It is this third type of jhāna that everyone agrees is necessary. The problem is with deciding which type of jhāna the Buddha is talking about in specific contexts. Since these three types of jhāna are not enumerated in the sutta pitaka, the debate centres around whether lokiya (mundane) samatha jhāna are necessary, since that is the only type of jhāna recognized by certain Buddhists.
This too can be seen as a misunderstanding, since samatha jhāna according to those who hold that it is not necessary is not exactly the same as jhāna according to those who hold that lokiya jhāna is.
According to those who say lokiya jhāna is necessary, they seem to believe that lokiya jhāna is a practice which allows for the realization of insight, in which case it cannot be samatha jhāna as understood by those who believe that samatha jhāna cannot lead directly to insight, unless the former group actually believes that jhāna based on a conceptual object can allow for the realization of insight into reality, which I'm pretty sure is not the case.
So, the debate is really not all it is cracked up to be, unless there are people who believe meditation based on a non-real conceptual object is sufficient for attainment of understanding of reality, in which case they are in contradiction with the sutta pitaka, not to mention the abhidhamma and commentaries.
I suppose there could still be room for debate over whether samatha jhāna based on a concept must be cultivated prior to Vipassana; the yuganaddha sutta probably shows this to be false:

Then there is the case where a monk has developed tranquillity preceded by insight. As he develops tranquillity preceded by insight, the path is born. He follows that path, develops it, pursues it. As he follows the path, developing it & pursuing it — his fetters are abandoned, his obsessions destroyed.
http://www.accesstoinsight.org/tipitaka/an/an04/an04.170.than.html

Of course for anyone actually adhering to the Theravada (I.e. the commentaries, patisambidhamagga, and abhidhamma), there isn't much room for controversy. Most of the debate is over whether to follow the existing commentaries or create one's own.

121: <p>I've found this to be an interesting question with highly respected monastics falling on both sides of the answer.</p>
 92: <p>Well, I think there is a reason why the path is eightfold and not sevenfold. The <em>Pāḷi Canon</em> is full of encouragements, made by the <em>Buddha</em>, to practice <em>jhānas</em>. It would be stretching the texts a lot to say it isn't necessary. I wouldn't argue over it though.</p>

<blockquote>
  <p>‘The sage, the withdrawn chief bull,<br>
  the <em>Buddha</em> who awakened to <em>jhāna</em>,<br>
  the One of Broad Wisdom has found<br>
  the opening amid confinement.’<br>
  -<a href="http://lirs.ru/lib/sutra/The_Numerical_Discourses_of_the_Buddha,Anguttara_Nikaya,Bodhi,2012.pdf#page=1318" rel="nofollow noreferrer"><em>AN 9.42, Confinement (Sambādha-suttaṃ)</em></a> &amp; <a href="http://lirs.ru/lib/sutra/Connected_Discourses_of_the_Buddha(Samyutta_Nikaya).Vol.I.pdf#page=71" rel="nofollow noreferrer"><em>SN 2.7, Pañcālacaṇḍa (Pañcālacaṇḍa-suttaṃ)</em></a>  </p>
</blockquote>

<hr>

<blockquote>
  <p>'There's no <em>jhāna</em> for one with no discernment,<br>
  no discernment for one
  with no <em>jhāna</em>.<br>
  But one with both <em>jhāna</em> &amp; discernment:<br>
  he's on the
  verge of Unbinding.'<br>
  -<a href="http://www.accesstoinsight.org/tipitaka/kn/dhp/dhp.25.than.html#dhp-372" rel="nofollow noreferrer"><em>Dhp v372</em></a></p>
</blockquote>
 471: <p>From <a href="https://suttacentral.net/sn55.5/en/sujato" rel="nofollow noreferrer">SN 55.5</a>:</p>
<blockquote>
<p>“Sir, the factors of stream-entry are associating with good people,
listening to the true teaching, <strong>proper attention</strong>, and practicing in
line with the teaching.”</p>
<p><em>“Sappurisasaṃsevo hi, bhante, sotāpattiyaṅgaṃ, saddhammassavanaṃ sotāpattiyaṅgaṃ, <strong>yonisomanasikāro</strong> sotāpattiyaṅgaṃ,
dhammānudhammappaṭipatti sotāpattiyaṅgan”ti.</em></p>
</blockquote>
<p>According to the sutta above, proper attention (<em>yonisomanasikāra</em>) is required for stream entry.</p>
<p>It's not possible to achieve proper attention, when one is afflicted with the <a href="https://en.wikipedia.org/wiki/Five_hindrances" rel="nofollow noreferrer">five hindrances</a>. In order to significantly overcome the five hindrances, one needs to have mastered at least the first jhana. You can find more info in <a href="https://buddhism.stackexchange.com/q/25011/471">this question</a>.</p>
<p>To quote Ven. Dhammavuddho from that question:</p>
<blockquote>
<p>The third condition, this word - yoniso manasikara, which I translate
as focused attention. Sometimes they say careful attention. This word
means that when you listen to the Dhamma, you are focused on listening
to the Dhamma. In other words, at that time, you don't have the five
hindrances. If that is so, then you can understand the Dhamma and
attain stream entry.</p>
<p>So who are the people who do not have the five hindrances? In the
suttas, it is stated by the Buddha that as long as a person has not
attained piti and sukha which are secluded from unwholesome states,
which are secluded from sensual pleasures, the five hindrances will
obsess him and obsess him habitually.</p>
<p>... When a person has attained the first jhana, he has eliminated the
five hindrances and the Buddha says that the five hindrances no longer
obsess that person habitually.</p>
<p>So there are two conditions if a person has the hindrances. Firstly,
it obsesses your mind, it enslaves your mind. Secondly, it is
habitual, it is very often there. ... When a person attains the first
jhana, these hindrances reduce to a very low level. ...</p>
</blockquote>
<p>In that question, Ven. Dhammavuddho claimed that instead of the first jhana, it is also possible that persons of high IQ can also achieve proper attention, although this is his personal opinion.</p>
<p>From this page on <a href="https://www.wisdomlib.org/definition/nirodha-samapatti" rel="nofollow noreferrer">Nirodha Samapatti</a>:</p>
<blockquote>
<p>According to Vis.M. XXIII, the entering into this state takes place in
the following way: by means of mental tranquillity (samatha) and
insight (vipassanā) one has to pass through all the 8 absorptions one
after the other up to the sphere of
neither-perception-nor-non-perception and then one has to bring this
state to an end. If, namely, according to the Vis.M., the disciple
(Anāgāmī or Arahat) passes through the absorption merely by means of
tranquillity, i.e. concentration, he will only attain the sphere of
neither-perception-nor-non-perception, and then come to a standstill;
<strong>if, on the other hand, he proceeds only with insight, he will reach
the fruition (phala) of Anāgāmī or Arahantship.</strong> He, however, who by
means of both faculties has risen from absorption to absorption and,
having made the necessary preparations, brings the sphere of
neither-perception-nor-non-perception to an end, such a one reaches
the state of extinction.</p>
</blockquote>
<p>So, according to the Visuddhimagga, the 8 jhanas and Nirodha Samapatti are not absolutely required for attainment of the fruition of anagami and arahat.</p>
 10100: <p>Upacara&amp;Appana Jhana are required for TanhaCarita according to Netti, Kayagatasatisutta's &amp;Mahasatipatthanasutta's  structure, Visuddhimagga DitthivisuddhiNiddesa.</p>
<p><a href="https://sutta.men/?rm.r.46.93...ta%E1%B9%87h%C4%81carito#hl" rel="nofollow noreferrer">Netti</a> (my english is terrible, so please find the translation yourself):</p>
<blockquote>
<p>[81] tattha diṭṭhicarito asmiṃ sāsane pabbajito sallekhānusantatavutti bhavati sallekhe tibbagāravo. taṇhācarito asmiṃ sāsane pabbajito sikkhānusantatavutti bhavati sikkhāya tibbagāravo. diṭṭhicarito sammattaniyāmaṃ okkamanto dhammānusārī bhavati. taṇhācarito sammattaniyāmaṃ okkamanto saddhānusārī bhavati, diṭṭhicarito sukhāya paṭipadāya dandhābhiññāya khippābhiññāya ca niyyāti. taṇhācarito dukkhāya paṭipadāya dandhābhiññāya khippābhiññāya ca niyyāti.</p>
<p>tattha kiṃkāraṇaṃ, yaṃ taṇhācarito dukkhāya paṭipadāya dandhābhiññāya khippābhiññāya ca niyyāti, tassa hi kāmā apariccattā bhavanti, so kāmehi viveciyamāno dukkhena paṭinissarati dandhañca dhammaṃ ājānāti? yo panāyaṃ diṭṭhicarito ayaṃ āditoyeva kāmehi anatthiko bhavati. so tato viveciyamāno khippañca paṭinissarati, khippañca dhammaṃ ājānāti. dukkhāpi paṭipadā duvidhā dandhābhiññā ca khippābhiññā ca. sukhāpi paṭipadā duvidhā dandhābhiññā ca khippābhiññā ca. sattāpi duvidhā mudindriyāpi tikkhindriyāpi. ye mudindriyā, te dandhañca paṭinissaranti dandhañca dhammaṃ ājānanti. ye tikkhindriyā, te khippañca paṭinissaranti, khippañca dhammaṃ ājānanti, imā catasso paṭipadā. ye hi keci niyyiṃsu vā niyyanti vā niyyissanti vā, te imāhi eva catūhi paṭipadāhi. evaṃ ariyā catukkamaggaṃ paññāpenti abudhajanasevitāya bālakantāya rattavāsiniyā nandiyā bhavataṇhāya avaṭṭanatthaṃ [āvaṭṭanatthaṃ (sī. ka.)]. ayaṃ vuccati nandiyāvaṭṭassa nayassa bhūmīti, tenāha ‘‘taṇhañca avijjampi ca samathenā’’ti.</p>
</blockquote>
<p>In DesanaHara, TanhaCarita should practice 4 Satipatthana and 4 Jhana. That is compatible with KayagatasatiSutta's commentary which separate Kayanupassana into 2 parts, Samatha and Vipassana.</p>
<p>The structure of KayagatasatiSutta is Samatha, and MahasatipattahanaSutta is Vipassana. This is compatible with many points of MahasatipattahanaSutta's commentary.</p>
<p>That's why in Visuddhimagga DitthivisuddhiNiddesa:</p>
<blockquote>
<p>and the purification of consciousness, namely, the eight attainments (Upacara Jhana) together with access concentration (Appana Jhana), has also been dealt with in detail in all its aspects in the Description of Concentration, (Chs. III to XIII) stated under the heading of “consciousness”</p>
</blockquote>
<hr />
<p>Don't combine and don't separate samatha-jhāna, vipassana-jhana,  and lokuttara-jhana without deep understand in the pali canon.</p>
<p>Samatha-jhāna and vipassana-jhana are friends who fight together to win, become Lokuttara-Jhana, <strong>together</strong>.</p>
<p><strong>Balava</strong> Vipassana-Jhana can't grow up with 5 hindrances. Samatha-jhāna can't  attain Nibbana without Understanding in the reality and 7 Anusaya. They are colleagues in the noble eightfold path.</p>
<p>Lokuttara-appana-jhana are them who graduated as a team, maggacittupada (<strong>a</strong> noble eightfold path; it is not many. It is only one team; it is &quot;ariyo atthangiko Maggo&quot;, not &quot;ariya atthangika magga&quot;).</p>
 18: <p>Actually, a point that is not well understood is that, among those who follow the Pali canon, there is no controversy over whether <em>some</em> jhāna is necessary; the answer is in all cases yes. The controversy is really over <em>which</em> jhāna is necessary.</p>

<p>There are three types of jhāna in total:</p>

<ol>
<li><strong>samatha-jhāna</strong> - jhāna based on a conceptual object that, due to its conceptual nature, cannot lead to the realization of the nature of reality.</li>
</ol>

<p>For example, in the Visuddhimagga:</p>

<blockquote>
  <p>The colour should not be reviewed. The characteristic should not be
  given attention. But rather, while not ignoring the colour, attention
  should be given by setting the mind on the [name] concept as the most
  outstanding mental datum, relegating the colour to the position of a
  property of its physical support. That [conceptual state] can be
  called by anyone he likes among the names for earth (pathavī) such as
  “earth” (pathavī), “the Great One” (mahī), “the Friendly One”
  (medinī), “ground” (bhūmi), “the Provider of Wealth” (vasudhā), “the
  Bearer of Wealth” (vasudharā), etc., whichever suits his manner of
  perception. Still “earth” is also a name that is obvious, so it can be
  developed with the obvious one by saying “earth, earth.” It should be
  adverted to now with eyes open, now with eyes shut. And he should go
  on developing it in this way a hundred times, a thousand times, and
  even more than that, until the learning sign arises.</p>
  
  <p><a href="http://static.sirimangalo.org/private/4.html" rel="nofollow">Path of Purification, IV.29</a></p>
</blockquote>

<p>2. <strong>vipassana-jhāna</strong> - jhāna based on ultimate reality that allows one to see the three characteristics and thus attain nibbana. As the Mahasi Sayadaw states:</p>

<blockquote>
  <p>The tranquillity that occurs while one contemplates various phenomena is called momentary concentration, the concentration that lasts momentarily during contemplation. No insight is possible without this momentary concentration. The meditator who has no basic [samatha] jhānic experience and relies on insight meditation alone develops insight through momentary concentration and attains the noble path. This concentration for insight is not confined to a single object. The meditator practising it notes all the mental and physical phenomena that arise. However, at the moment of noting, his mind is fixed on the object and free from distraction. This is obvious to the meditator who practises effectively.</p>
  
  <p><a href="http://www.aimwell.org/sallekha.html" rel="nofollow">http://www.aimwell.org/sallekha.html</a></p>
</blockquote>

<p>3. <strong>lokuttara-jhāna</strong> - jhāna that takes a supermundane object (nibbana), and is equivalent to attaining the noble path and fruition. According to Bhante Gunaratana:</p>

<blockquote>
  <p>But the four jhanas again reappear in a later stage in the development of the path, in direct association with liberating wisdom, and they are then designated the supramundane (lokuttara) jhanas. These supramundane jhanas are the levels of concentration pertaining to the four degrees of enlightenment experience called the supramundane paths (magga) and the stages of liberation resulting form them, the four fruits (phala).</p>
  
  <p><a href="http://www.budsas.org/ebud/jhanas/jhanas01.htm" rel="nofollow">http://www.budsas.org/ebud/jhanas/jhanas01.htm</a></p>
</blockquote>

<p>It is this third type of jhāna that everyone agrees is necessary. The problem is with deciding which type of jhāna the Buddha is talking about in specific contexts. Since these three types of jhāna are not enumerated in the sutta pitaka, the debate centres around whether lokiya (mundane) samatha jhāna are necessary, since that is the only type of jhāna recognized by certain Buddhists.</p>

<p>This too can be seen as a misunderstanding, since samatha jhāna according to those who hold that it is not necessary is not exactly the same as jhāna according to those who hold that lokiya jhāna is.</p>

<p>According to those who say lokiya jhāna is necessary, they seem to believe that lokiya jhāna is a practice which allows for the realization of insight, in which case it cannot be samatha jhāna as understood by those who believe that samatha jhāna cannot lead directly to insight, unless the former group actually believes that jhāna based on a conceptual object can allow for the realization of insight into reality, which I'm pretty sure is not the case.</p>

<p>So, the debate is really not all it is cracked up to be, unless there are people who believe meditation based on a non-real conceptual object is sufficient for attainment of understanding of reality, in which case they are in contradiction with the sutta pitaka, not to mention the abhidhamma and commentaries.</p>

<p>I suppose there could still be room for debate over whether samatha jhāna based on a concept must be cultivated prior to Vipassana; the yuganaddha sutta probably shows this to be false:</p>

<blockquote>
  <p>Then there is the case where a monk has developed tranquillity preceded by insight. As he develops tranquillity preceded by insight, the path is born. He follows that path, develops it, pursues it. As he follows the path, developing it &amp; pursuing it — his fetters are abandoned, his obsessions destroyed.</p>
  
  <p><a href="http://www.accesstoinsight.org/tipitaka/an/an04/an04.170.than.html" rel="nofollow">http://www.accesstoinsight.org/tipitaka/an/an04/an04.170.than.html</a></p>
</blockquote>

<p>Of course for anyone actually adhering to the Theravada (I.e. the commentaries, patisambidhamagga, and abhidhamma), there isn't much room for controversy. Most of the debate is over whether to follow the existing commentaries or create one's own.</p>
