MN 18 must vedana precede sañña?

Interesting question a friend asked me:

I have a question. In MN 18 there is this formula:
eye + forms + consciousness → contact → feel → perceive → think → proliferate
But does this apply to all perceptions? For example, I see a red car on the street. Will there be any feeling that leads to the perception "This is a red car"?
If the perception is "This is a beautiful/ugly car" however, then I see why there is feeling first. Well, not sure. This matter is complex for me.

(6aya. Eye base)

Cakkhuñc-āvuso, paṭicca rūpe ca uppajjati cakkhu-viññāṇaṃ,	Eye consciousness arises dependent on the eye and sights.
tiṇṇaṃ saṅgati phasso,	The meeting of the three is contact.
phassa-paccayā vedanā,	Contact is a condition for feeling.
yaṃ vedeti taṃ sañjānāti,	What you feel, you perceive.
yaṃ sañjānāti taṃ vitakketi,	What you perceive, you think about.
yaṃ vitakketi taṃ papañceti,	What you think about, you proliferate.
yaṃ papañceti tato-nidānaṃ	What you proliferate about is the source
purisaṃ papañca-saññā-saṅkhā samudācaranti	from which a person is beset by concepts of identity that emerge from the proliferation of perceptions.
atīt-ānāgata-paccuppannesu cakkhu-viññeyyesu rūpesu.	This occurs with respect to sights known by the eye in the past, future, and present.

frankk response:

concsciousness is knowing at a raw sensory data level, 

vedana and perception happen after contact (phassa) whereas consciousness precedes contact, 

so vedana and sañña involve the 'knowing' from consciousness but with some thing extra added, such as memory associations, labeling, discrimination, etc.

There are suttas where it states phassa as the proximate cause for vedana and sañña indvidually, so I don't think vedana must precede sañña as MN 18 implies.

I think what the hierarchy from MN 18 is showing is that perception, to do its job, has more stuff added and processing to do its job, compared to vedana which adds less stuff to the cognized knowing to perform it's job. 

For your question example with the red car, I would argue that perception and feeling both are operating at the same hierarchy level, both adding information to basic cognition before contact.

You would have to perceive and understand the value of a red car to generate feelings of like or aversion, otherwise why would a hunk of red metal shaped like a car make you feel anything?

verb forms of consciousness, feeling, perception, wisdom

vijānāti 1
pr. (+acc) comprehends; understands; recognises; distinguishes; is aware (of) [vi + √ñā + nā + ti] ✓

vedeti 1
pr. (+acc) feels; experiences; senses; notices [√vid + *e + ti] ✓
grammarexamplesconjugationroot familyfrequencyfeedback
vedeti 2
pr. (+acc) knows; understands; learns about [√vid + *e + ti] ✓

sañjānāti
pr. (+acc) knows; knows as; perceives; conceives; recognizes [saṃ + √ñā + nā + ti] ✓

pajānāti

pr. (+acc) knows; knows clearly; understands; distinguishes [pa + √ñā + nā + ti] ✓

Notice they all have the same root √ñā, except vedana has √vid

Roots

√vid 1

root. √vid･8 e, aya (know, sense, feel) 66

ñā

root. (gram) √ñā (know) [√ñā + ā] ✓

MN 43 probably gives the closest to an answer

43.2 - (Viññāṇa: Consciousness)

43.2.1 – (defined in terms of cognizing 3 types of vedana)

“‘Viññāṇaṁ viññāṇan’ti, āvuso, vuccati. Kittāvatā nu kho, āvuso, viññāṇanti vuccatī”ti?	“They speak of ‘consciousness’. How is consciousness defined?”
“‘Vijānāti vijānātī’ti kho, āvuso, tasmā viññāṇanti vuccati. Kiñca vijānāti? Sukhantipi vijānāti, dukkhantipi vijānāti, adukkhamasukhantipi vijānāti. ‘Vijānāti vijānātī’ti kho, āvuso, tasmā viññāṇanti vuccatī”ti.	“It’s called consciousness because it cognizes. And what does it cognize? It cognizes ‘pleasure’ and ‘pain’ and ‘neutral’. It’s called consciousness because it cognizes.”

43.2.2 – (viññāṇa can not be separated from pañña)

“Yā cāvuso, paññā yañca viññāṇaṁ— ime dhammā saṁsaṭṭhā udāhu visaṁsaṭṭhā? Labbhā ca panimesaṁ dhammānaṁ vinibbhujitvā vinibbhujitvā nānākaraṇaṁ paññāpetun”ti? Variant: vinibbhujitvā vinibbhujitvā → vinibbhujjitvā vinibbhujjitvā (mr)

“Wisdom and consciousness—are these things mixed or separate? And can we completely dissect them so as to describe the difference between them?”

“Yā cāvuso, paññā yañca viññāṇaṁ— ime dhammā saṁsaṭṭhā, no visaṁsaṭṭhā. Na ca labbhā imesaṁ dhammānaṁ vinibbhujitvā vinibbhujitvā nānākaraṇaṁ paññāpetuṁ. Yaṁ hāvuso, pajānāti taṁ vijānāti, yaṁ vijānāti taṁ pajānāti. Variant: Yaṁ hāvuso → yañcāvuso (bj, mr); yañca āvuso (sya-all, km)Tasmā ime dhammā saṁsaṭṭhā, no visaṁsaṭṭhā. Na ca labbhā imesaṁ dhammānaṁ vinibbhujitvā vinibbhujitvā nānākaraṇaṁ paññāpetun”ti.

“Wisdom and consciousness—these things are mixed, not separate. And you can never completely dissect them so as to describe the difference between them. For you understand what you cognize, and you cognize what you understand. That’s why these things are mixed, not separate. And you can never completely dissect them so as to describe the difference between them.”

43.2.3 – (viññāña should be known, pañña developed)

“Yā cāvuso, paññā yañca viññāṇaṁ— imesaṁ dhammānaṁ saṁsaṭṭhānaṁ no visaṁsaṭṭhānaṁ kiṁ nānākaraṇan”ti?	“Wisdom and consciousness—what is the difference between these things that are mixed, not separate?”
“Yā cāvuso, paññā yañca viññāṇaṁ— imesaṁ dhammānaṁ saṁsaṭṭhānaṁ no visaṁsaṭṭhānaṁ paññā bhāvetabbā, viññāṇaṁ pariññeyyaṁ. Idaṁ nesaṁ nānākaraṇan”ti.	“The difference between these things is that wisdom should be developed, while consciousness should be completely understood.”

43.3 - (vedana: sensation. Senses sukha, dukkha, neither)

“‘Vedanā vedanā’ti, āvuso, vuccati. Kittāvatā nu kho, āvuso, vedanāti vuccatī”ti?	“They speak of this thing called ‘feeling’. How is feeling defined?”
“‘Vedeti vedetī’ti kho, āvuso, tasmā vedanāti vuccati. Kiñca vedeti? Sukhampi vedeti, dukkhampi vedeti, adukkhamasukhampi vedeti. ‘Vedeti vedetī’ti kho, āvuso, tasmā vedanāti vuccatī”ti.	“It’s called feeling because it feels. And what does it feel? It feels pleasure, pain, and neutral. It’s called feeling because it feels.”

43.4 - (sañña: Perception)

43.4.1 – (perceives 5 colors)

“‘Saññā saññā’ti, āvuso, vuccati. Kittāvatā nu kho, āvuso, saññāti vuccatī”ti?	“They speak of this thing called ‘perception’. How is perception defined?”
“‘Sañjānāti sañjānātī’ti kho, āvuso, tasmā saññāti vuccati. Kiñca sañjānāti? Nīlakampi sañjānāti, pītakampi sañjānāti, lohitakampi sañjānāti, odātampi sañjānāti. ‘Sañjānāti sañjānātī’ti kho, āvuso, tasmā saññāti vuccatī”ti.	“It’s called perception because it perceives. And what does it perceive? It perceives blue, yellow, red, and white. It’s called perception because it perceives.”

43.4.2 – (sañña can not be separted from vedana)

“Yā cāvuso, vedanā yā ca saññā yañca viññāṇaṁ— ime dhammā saṁsaṭṭhā udāhu visaṁsaṭṭhā? Labbhā ca panimesaṁ dhammānaṁ vinibbhujitvā vinibbhujitvā nānākaraṇaṁ paññāpetun”ti?

“Feeling, perception, and consciousness—are these things mixed or separate? And can we completely dissect them so as to describe the difference between them?”

“Yā cāvuso, vedanā yā ca saññā yañca viññāṇaṁ— ime dhammā saṁsaṭṭhā, no visaṁsaṭṭhā. Na ca labbhā imesaṁ dhammānaṁ vinibbhujitvā vinibbhujitvā nānākaraṇaṁ paññāpetuṁ. Yaṁ hāvuso, vedeti taṁ sañjānāti, yaṁ sañjānāti taṁ vijānāti. Variant: Yaṁ hāvuso → yaṁ cāvuso (sya-all, km); yañcāvuso (mr)Tasmā ime dhammā saṁsaṭṭhā no visaṁsaṭṭhā. Na ca labbhā imesaṁ dhammānaṁ vinibbhujitvā vinibbhujitvā nānākaraṇaṁ paññāpetun”ti.

“Feeling, perception, and consciousness—these things are mixed, not separate. And you can never completely dissect them so as to describe the difference between them. For you perceive what you feel, and you cognize what you perceive. That’s why these things are mixed, not separate. And you can never completely dissect them so as to describe the difference between them.”

Forum discussion

https://www.reddit.com/r/theravada/comments/16p6vqw/comment/k2dsm9k/?context=3
level 1

Substantial-Deal3567·8 hr. ago

we have MN 148 which details the mental process from the sense bases contact to the underlying tendencies to greed, hatred and delusion. These tendencies lead to proliferated perception (SN 35.94).

SN 35.93 describes the activities that follow contact. It seems they happen at the same time.
Contacted, one feels. Contacted, one intends. Contacted, one perceives.

Aniccaṃ kho pana, bhikkhave, paccayaṃ paṭicca uppanno cakkhusamphasso kuto nicco bhavissati.	But since eye contact has arisen dependent on conditions that are impermanent, how could it be permanent?
Phuṭṭho, bhikkhave, vedeti, phuṭṭho ceteti, phuṭṭho sañjānāti.	Contacted, one feels, intends, and perceives.
Itthetepi dhammā calā ceva byathā ca aniccā vipariṇāmino aññathābhāvino … pe …	So these things are tottering and toppling; they’re impermanent, perishing, and changing.