The oneness of nature does not result from division, or from union or from community of possession, but from one nature being proper to both Father and Son.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic union oneness
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

“"It would be prejudicial to holy things, if we had to do away with them, just because some do not think them holy. So if some misunderstand homoousion, what is that to me, if I understand it rightly? . . . The oneness of nature does not result from division, or from union or from community of possession, but from one nature being proper to both Father and Son." _______________________ THIRD ARTICLE [I, Q. 39, Art. 3] Whether Essential Names Should Be Predicated in the Singular of the Three Persons? Objection 1: It would seem that essential names, as the name "God,"” source