What is "dualistic theory"

Dualistic \Du`al*is"tic\, a. Consisting of two; pertaining to dualism or duality.

Dualistic system or Dualistic theory (Chem.), an old theory, originated by Lavoisier and developed by Berzelius, that all definite compounds are binary in their nature, and consist of two distinct constituents, themselves simple or complex, and possessed of opposite chemical or electrical affinities; -- superseded by later developments in chemical bonding theory, especially quantum mechanics.