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.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic reality pleasure
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“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) .” source