A thing's particular nature is its own power of action and self-preservation.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic action power
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

“Therefore the human body is naturally incorruptible. I answer that, We may speak of any corruptible thing in two ways; first, in respect of its universal nature, secondly, as regards its particular nature. A thing's particular nature is its own power of action and self-preservation. And in respect of this nature, every corruption and defect is contrary to nature, as stated in De Coelo ii, text. 37, since this power tends to the being and preservation of the thing to which it belongs.” source