_I answer that,_ Pleasure can be considered in two ways; first, as
existing in reality; secondly, as existing in the memory. Again
thirst, or desire, can be taken in two ways; first, properly, as
denoting a craving for something not possessed; secondly, in general,
as excluding distaste.

Considered as existing in reality, pleasure does not of itself cause
thirst or desire for itself, but only accidentally; provided we take
thirst or desire as denoting a craving for some thing not possessed:
because pleasure is an emotion of the appetite in respect of
something actually present. But it may happen that what is actually
present is not perfectly possessed: and this may be on the part of
the thing possessed, or on the part of the possessor. On the part of
the thing possessed, this happens through the thing possessed not
being a simultaneous whole; wherefore one obtains possession of it
successively, and while taking pleasure in what one has, one desires
to possess the remainder: thus if a man is pleased with the first
part of a verse, he desires to hear the second part, as Augustine
says (Confess. iv, 11). In this way nearly all bodily pleasures cause
thirst for themselves, until they are fully realized, because
pleasures of this kind arise from some movement: as is evident in
pleasures of the table. On the part of the possessor, this happens
when a man possesses a thing which is perfect in itself, yet does not
possess it perfectly, but obtains possession of it little by little.
Thus in this life, a faint perception of Divine knowledge affords us
delight, and delight sets up a thirst or desire for perfect
knowledge; in which sense we may understand the words of Ecclus.
24:29: "They that drink me shall yet thirst."

On the other hand, if by thirst or desire we understand the mere
intensity of the emotion, that excludes distaste, thus more than all
others spiritual pleasures cause thirst or desire for themselves.
Because bodily pleasures become distasteful by reason of their
causing an excess in the natural mode of being, when they are
increased or even when they are protracted; as is evident in the case
of pleasures of the table. This is why, when a man arrives at the
point of perfection in bodily pleasures, he wearies of them, and
sometimes desires another kind. Spiritual pleasures, on the contrary,
do not exceed the natural mode of being, but perfect nature. Hence
when their point of perfection is reached, then do the