The word "kaya" appears to be used in various ways in the suttas. It can mean:
- "Physical body", such as in Kimsuka Sutta & Assutavā Sutta, as follows:
‘City’ is a term for this body made up of the four primary elements,
produced by mother and father, built up from rice and porridge, liable
to impermanence, to wearing away and erosion, to breaking up and
‘nagaran’ti kho, bhikkhu, imassetaṃ cātumahābhūtikassa kāyassa
adhivacanaṃ mātāpettikasambhavassa odanakummāsūpacayassa aniccucchādanaparimaddanabhedanaviddhaṃsanadhammassa.
Mendicants, when it comes to this body made up of the four primary
elements, an uneducated ordinary person might become disillusioned,
dispassionate, and freed.
“assutavā, bhikkhave, puthujjano imasmiṃ cātumahābhūtikasmiṃ
kāyasmiṃ nibbindeyyapi virajjeyyapi vimucceyyapi
But an uneducated ordinary person would be better off taking this
body made up of the four primary elements to be their self, rather than the mind.
Varaṃ, bhikkhave, assutavā puthujjano imaṃ cātumahābhūtikaṃ kāyaṃ
attato upagaccheyya, na tveva cittaṃ.
Why is that?
Taṃ kissa hetu?
This body made up of the four primary elements is seen to last for
a year, or for two, three, four, five, ten, twenty, thirty, forty,
fifty, or a hundred years, or even longer.
Dissatāyaṃ, bhikkhave, cātumahābhūtiko kāyo ekampi vassaṃ
tiṭṭhamāno dvepi vassāni tiṭṭhamāno tīṇipi vassāni tiṭṭhamāno
cattāripi vassāni tiṭṭhamāno pañcapi vassāni tiṭṭhamāno dasapi vassāni
tiṭṭhamāno vīsatipi vassāni tiṭṭhamāno tiṃsampi vassāni tiṭṭhamāno
cattārīsampi vassāni tiṭṭhamāno paññāsampi vassāni tiṭṭhamāno
vassasatampi tiṭṭhamāno, bhiyyopi tiṭṭhamāno.
- "Grouping" of aggregates, such as in MN 44, as follows:
Visākha, the Buddha said that these five grasping aggregates are
“Pañca kho ime, āvuso visākha, upādānakkhandhā sakkāyo vutto
- "Grouping" of similar types of phenomena, such as in DN 15, as follows:
Suppose there were none of the features, attributes, signs, and
details by which the categories of mental or physical phenomena are
found. Would either linguistic contact or impingement contact still be
“Yehi, ānanda, ākārehi … pe … yehi uddesehi nāmakāyassa ca
rūpakāyassa ca paññatti hoti, tesu ākāresu … pe … tesu uddesesu asati
api nu kho adhivacanasamphasso vā paṭighasamphasso vā paññāyethā”ti?
- "Grouping" of specific types of phenomena, such as in MN 118, as follows:
I tell you, monks, that this — in-&-out breaths — are classed as a body among bodies
Kāyesu kāyaññatarāhaṃ, bhikkhave, evaṃ vadāmi yadidaṃ—assāsapassāsā.
To answer the question asked, as demonstrated in the examples above, it appears a "kaya" ("grouping") is made up of various khandhas or even subsets of one khandha (such as the four elements) but a kaya is not necessarily made up of all five khandhas.
This appears to be the difference between "Khandha" and "Kaya", which also shows the words are not necessarily related.
As for the author Tse-fu Kuan, based in the paragraphs quoted at the bottom below, he appears to be attempting to define the word "kaya" in one way, which appears incorrect.
Also, in the context of Satipatthana, the word "kaya" does not mean "the individual" (as it does in MN 44 cited above), as Tse-fu Kuan appears to propose. Both the Satipatthana & Anapanasati suttas clearly distinguish between kayanupassana, vedanuspassana, cittanupassana & dhammanupassana.
In the context of Satipatthana/Anapanasati, the word "kaya" in the 1st tetrad refers three types of kaya, namely: (i) nama-kaya - the mind; (ii) assāsapassāsā-kaya - the breathing; and (iii) rupa-kaya - the physical body.
It follows the 3rd step of Anapanasati is defined as "sabbakāyapaṭisaṃvedī", which means "experiencing all bodies/groups". This means experiencing how the state of mind effects/conditions the breathing; and how, in turn, the state of the breathing effects/conditions the physical body; and how, in turn, the state of the breathing & body effects/conditions the mind.
As for Tse-fu Kuan reference to the Balapandita Sutta (SN 12.19), the "kaya" here never meant a "sentient being capable of consciousness". This is ridiculous because SN 23.2 defines "a being" as "strong attachment". The word "kaya" in SN 12.19 merely refers to the grouping of the five aggregates.
Thus, SN 12.19 says: "there is this kaya (internal five aggregates) and external namarupa (external minds & bodies). Based on these two things, there is sense contact".
Based on Chinese versions Kuan argues that Kayagatasati originally
meant not just mindfulness of the body, but had a similar meaning as
Satipatthana. He believes that Anapanasati Sutta contains the oldest
of the teachings on mindfulness, and Satipatthana Sutta the latest -
derived from several older sources.
The analysis shows that kaayagataa sati and the four satipa.t.thaanas are two different ways of formulating the teaching on mindfulness
according to different schemes of classification of phenomena.
a further examination of the canonical contexts
in which kAyagatA sati and kAyasati occur shows that kAya here refers to an
individual that can experience through his senses. KAyagatA sati or kAyasati
is mindfulness directed to kAya, the locus of our subjective experience based
on the senses. It can transform our subjective experience, and thereby
enable us to achieve liberation. It is a general guideline or fundamental principle applied to the path to liberation, and is not restricted to those specific
exercises given in different versions of the KAyagatAsati Sutta
All the above discussions lead to the conclusion that kAyagatA sati and the four satipaWWhAnas are two different ways of
formulating the teaching on mindfulness according to different schemes of
classification of phenomena, which cover the individual and the external world
perceived. Both kAyagatA sati and the four satipaWWhAnas concern subject-object
interaction, where lies the crux of saSsAra as well as nirvana.
KAyasati and kAyagatA sati are usually rendered as “mindfulness of the body”
and “mindfulness concerning the body” respectively. Chapter 4 will show
that kAya here refers to the “individual” rather than the “body.”
Chapter 4 will show
that kAya here refers to the “individual” rather than the “body.” I will leave
the two terms untranslated. This function of sati is elucidated in the
Kimsuka Sutta, which follows the Dukkhadhamma Sutta. Here the Buddha
makes a simile as follows: A king has a frontier city with six gates. The gatekeeper keeps out strangers and admits acquaintances. The Buddha explains
that, in this simile, “the city” is a designation for kAya; “the six gates” stand
for the six internal sense bases; “the gatekeeper” represents sati (SN IV 194)