Lance Cousins has a very thorough discussion of this term in his article
"Good or Skilful? Kusala in Canon and Commentary", published in the online
Journal of Buddhist Ethics: http://jbe.gold.ac.uk/3/cousins1.html

Extract:

Damien Keown comments that:

"....the most natural translation for kusala when used in a moral context is
"virtue" or "goodness". It is very common for kusala to be rendered as
"skilful", but it should be recognised that this translation carries with
it a specific implication for the nature of Buddhist ethics, namely that it
is utilitarian." (1)

In fact, I am not convinced that a utilitarian implication does in fact
necessarily follow. Skill, let alone wisdom, can be valued for more reasons
than utilitarian ones. Keown then distinguishes what he calls the moral and
the technical senses of the word kusala and argues strongly against
translating it as "skilful":

"Although I have no statistics to back this up there can be little doubt
that in the Nikaayas the occurrences of kusala in a technical context are
massively outnumbered by those in a moral context. So why, when translating
the term into English, is the tail allowed to wag the dog and the moral
sense suppressed in favour of the technical one?"

He goes on to point out:

"The problem with using "skilful" as a translation of kusala is that whereas
both "good" and "kusala" extend in their respective languages to both moral
and technical commendation, the English word "skilful" does not. "Skilful"
denotes approval in the technical sense only and does not figure at all in
the vocabulary of moral discourse in English."

As Keown indicates, the use of "skilful" is stylistically slightly
unnatural here in terms of English usage. Perhaps, however, this only shows
that Buddhist concepts are themselves unfamiliar to ordinary English usage
and we should be cautious about adopting concepts with many hidden
implications, deriving from a long history of European theological and
philosophical debate. In fact I think that the use in the Buddhist
literature is rather more complex than Keown allows and deserves to be
investigated more fully. Here I shall look first at the commentarial
account and then turn to the earlier sources.

Kusala in the commentarial sources

In the commentary to the Diigha-nikaaya Buddhaghosa gives five senses of
the word kusala: (2)

aarogya absence of illness, health

anavajja (originally) not reprehensible, blameless; (later)

kosalla-sambhuuta produced by skill

niddaratha freedom from distress

sukha-vipaaka bringing pleasant results

The first of these he attributes to the Jaataka method of exposition
(pariyaaya) and in fact it is clear that this represents a normal Indian
usage, rather than a technical sense of Buddhist thought. (3) What is
referred to is such expressions as kacci nu kusala.m meaning "Are you
well?" or something similar, usually found in verse texts. This usage is
indeed particularly common in the Jaatakas. (4) The second meaning
Buddhaghosa refers to as the Suttanta method of exposition; it is often
applied by him in the exegesis of particular sutta passages. (5) Sometime
this is referred to as the Baahitika-sutta(nta) method of exposition. (6)

The remaining three senses are all attributed by Buddhaghosa to the
Abhidhamma method of exposition. In fact the fourth: "freedom from
distress" is rather unusual and seems to be dropped by the later
commentarial tradition. (7) Indeed Buddhaghosa himself does not use it and
the .tiikaa writer cannot offer a source passage to illustrate it. (8) For
present purposes we can disregard this meaning. The fifth we can also put
on one side. The notion that skilful actions bring pleasant results is of
course well-established, but it is noticeable that the commentators do not
in fact often explain the word kusala as having this sense. (9) It is clear
that Buddhaghosa has placed it in an abhidhamma context because of the
importance of this idea to understanding the first triplet of the
abhidhamma-maatikaa.

The .tiikaa writer's first comment on Buddhaghosa's explanation of kusala
is to ask why the sense of cheka "skilled" is not given as a sixth meaning.
This is indeed surprising; for this explanation is given by Buddhaghosa and
other commentators in a number of contexts, including some cases where the
word is used in what Keown calls its technical sense. (10) However, the
..tiikaa writer answers his own question by pointing out that this sense is
included in the third meaning given by Buddhaghosa: "produced by skill" and
hence is not taken separately. Skill of course is listed in the abhidhamma
register for understanding (pa~n~naa) and so the intended meaning is
"produced by wisdom ". The .tiikaa writer explains this as equivalent to
"caused by appropriate bringing to mind" (yoniso-manasik aara-hetuka).

In fact this explanation of kusala as "produced by skill " is used in
non-abhidhamma contexts also, as well as in explanations of akusala
"unskilful". (11) Moreover, there are also contexts where the sense of
expert (pa.n.dita) is given, but seems to converge on the sense of "wise"
or "knowledgeable".(12) Closely related to this are passages where the
expression "skilful dhammas" is explained as referring to the dhammas which
contribute to awakening (bodhipakkhiya). (13)

The author of the Abhidhamma commentary, probably a senior contemporary of
Buddhaghosa, (14) takes a slightly different approach. (15) He offers just
three senses: 1. health; 2. faultless; 3. produced by skill. He too relates
the first to the Jaataka method of exposition and the second to the
Baahitika-sutta method of exposition. (He cannot explicitly relate it to
the Suttanta method, as he wishes to argue that it is found in Abhidhamma.)
Again like Buddhaghosa, he links the third to the Abhidhamma method of
exposition and then addresses the obvious problem that this creates; for
wisdom would be expected to lead to consciousness connected with knowledge
(~naa.nasampayutta), but not to that which lacks knowledge. Yet the term
"skilful" in abhidhamma is also applied to two-rooted consciousness which
is without knowledge.

The commentator argues that even this can be called skilful by convention.
He gives the example of a palm-leaf fan which is still given that name even
when made out of other materials. He agrees, however, that in terms of
strict abhidhamma (nippariy aayena) only consciousness with knowledge can
be called skilful in all three senses. In the case of consciousness without
knowledge only the two senses of health and faultless strictly apply. The
inclusion of the sense of "health " here is of course good hermeneutics; in
fact, however, its inclusion as a sense of kusala must be a later
development, derived from the kind of expression mentioned above.

Surprisingly, however, this is the Abhidhamma commentator's second
discussion of the meanings of the word kusala. In an earlier passage he
gives four senses: (16)

aarogya absence of illness, health

anavajja not reprehensible, blameless; faultless

cheka skilled

sukha-vipaaka bringing pleasant results

Exactly this list is given also by Buddhadatta and by Mahaanaama. (17) It
seems to be standard for later writers. (18) For most sources the third
meaning is excluded for the main abhidhamma contexts (19) and this view is
adopted by many modern commentators. (20) The general acceptance of this
set of three probably derives from its occurrence in the Mahaa.tiikaa to
the Visuddhimagga (attr. Dhammapaala). (21) Buddhadatta, however, allows
only the two senses of "faultless" and "bringing wished for results"
(i.t.tha-vipaaka).

Why then does the Abhidhamma commentary offer two different explanations?
This must be because in the earlier passage it is commenting on kusalaa
dhammaa in the first triplet of the Maatikaa, whereas the later passage
refers to kusala.m citta.m in the dhammuddesa of the first type of
consciousness i.e. that connected with knowledge. This will in part account
for the inclusion of "produced by skill" as a meaning of kusala. However,
it must also have been embedded in his source material; (22) here, as
elsewhere, the Abhidhamma commentary preserves material for us in a less
digested form as against the more carefully styled writings of Buddhaghosa.

There is perhaps more to it than this. The Pali abhidhamma system is
unusual in allowing skilful consciousness without knowledge. In the
Sarvaastivaadin system, for example, knowledge is a universal and so there
cannot be skilful consciousness without it. It may be that at an earlier
stage the connexion between the skilful and wisdom was felt more strongly.
That said, the commentaries do preserve the link. In the mnemonic exegesis
of the word kusala, the first two syllables are sometimes taken as a word
kusa, meaning "wisdom " (cp. Skt ku"saagra). (23) No doubt too the question
of how far even skilful consciousness can be entirely unrelated to wisdom
is closely connected to the issue as to whether faith (saddhaa) that is not
based on wisdom can occur.

In summary then, it seems that the commentators (except perhaps Buddhaghosa
himself) would probably not have disagreed with Damien Keown's remarks:

No-one would describe a simple act of generosity as a "skilful deed", and
who has ever heard of a boy scout doing his "skilful deed for the day" ?
Instead, one naturally speaks of "good" or "virtuous" deeds." (24)


[The article continues in much the same vein for another twenty pages]

Best wishes,

Robert