The Complete Aristotle (eng.)

uniformly, either
always or usually. There is no need to discuss in exact detail the
things that happen contrary to nature, nor to ask whether they
happen in some sense naturally or from some other cause; it would
seem that chance is at least partly the cause of such events. Those
things happen through compulsion which take place contrary to the
desire or reason of the doer, yet through his own agency. Acts are
done from habit which men do because they have often done them
before. Actions are due to reasoning when, in view of any of the
goods already mentioned, they appear useful either as ends or as
means to an end, and are performed for that reason: ‘for that
reason,’ since even licentious persons perform a certain number of
useful actions, but because they are pleasant and not because they
are useful. To passion and anger are due all acts of revenge.
Revenge and punishment are different things. Punishment is
inflicted for the sake of the person punished; revenge for that of
the punisher, to satisfy his feelings. (What anger is will be made
clear when we come to discuss the emotions.) Appetite is the cause
of all actions that appear pleasant. Habit, whether acquired by
mere familiarity or by effort, belongs to the class of pleasant
things, for there are many actions not naturally pleasant which men
perform with pleasure, once they have become used to them. To sum
up then, all actions due to ourselves either are or seem to be
either good or pleasant. Moreover, as all actions due to ourselves
are done voluntarily and actions not due to ourselves are done
involuntarily, it follows that all voluntary actions must either be
or seem to be either good or pleasant; for I reckon among goods
escape from evils or apparent evils and the exchange of a greater
evil for a less (since these things are in a sense positively
desirable), and likewise I count among pleasures escape from
painful or apparently painful things and the exchange of a greater
pain for a less. We must ascertain, then, the number and nature of
the things that are useful and pleasant. The useful has been
previously examined in connexion with political oratory; let us now
proceed to examine the pleasant. Our various definitions must be
regarded as adequate, even if they are not exact, provided they are
clear.
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    We may lay it down that Pleasure is a movement, a movement by
which the soul as a whole is consciously brought into its normal
state of being; and that Pain is the opposite. If this is what
pleasure is, it is clear that the pleasant is what tends to produce
this condition, while that which tends to destroy it, or to cause
the soul to be brought into the opposite state, is painful. It must
therefore be pleasant as a rule to move towards a natural state of
being, particularly when a natural process has achieved the
complete recovery of that natural state. Habits also are pleasant;
for as soon as a thing has become habitual, it is virtually
natural; habit is a thing not unlike nature; what happens often is
akin to what happens always, natural events happening always,
habitual events often. Again, that is pleasant which is not forced
on us; for force is unnatural, and that is why what is compulsory,
painful, and it has been rightly said
All that is done on compulsion is bitterness unto the soul.
    So all acts of concentration, strong effort, and strain are
necessarily painful; they all involve compulsion and force, unless
we are accustomed to them, in which case it is custom that makes
them pleasant. The opposites to these are pleasant; and hence ease,
freedom from toil, relaxation, amusement, rest, and sleep belong to
the class of pleasant things; for these are all free from any
element of compulsion. Everything, too, is pleasant for which we
have the desire within us, since desire is the craving for
pleasure. Of the desires some are irrational, some associated with
reason. By irrational I mean those which do not arise from any
opinion held by the mind. Of this kind are those known as
‘natural’; for instance, those originating in the body, such as the
desire for nourishment, namely hunger and thirst, and a separate
kind of desire answering to each kind of nourishment; and the
desires connected with taste and sex and sensations of touch in
general; and those of smell, hearing, and vision. Rational desires
are those which we are induced to have; there are many things we
desire to see or get because we have been told of them and induced
to believe them