We understand one thing only when we understand by one idea
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic understanding ideas
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17611/pg17611-images.html

Context

“Now it was shown above that things seen in God, are not seen singly by their own similitude; but all are seen by the one essence of God. Hence they are seen simultaneously, and not successively. Reply Obj. 1: We understand one thing only when we understand by one idea; but many things understood by one idea are understood simultaneously, as in the idea of a man we understand "animal" and "rational"; and in the idea of a house we understand the wall and the roof. Reply Obj.” source