Therefore neither can man, who is of rational nature, attain the end of the intellectual nature, which is Happiness.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic happiness
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

“For just as the rational is above the sensible nature, so the intellectual is above the rational, as Dionysius declares (Div. Nom. iv, vi, vii) in several passages. But irrational animals that have the sensitive nature only, cannot attain the end of the rational nature. Therefore neither can man, who is of rational nature, attain the end of the intellectual nature, which is Happiness. Obj. 2: Further, True Happiness consists in seeing God, Who is pure Truth. But from his very nature, man considers truth in material things: wherefore "he understands the intelligible species in the phantasm"” source