De Plantatione

According to the other meaning, as in the disputes of dialecticians, the word "undemonstrated" is used in a double sense, either of a proposition which it is hard to demonstrate by reason of its difficulty, or of one which is intrinsically so plain as to require no demonstration, and the truth of which is established not by the testimony of any one else, but by its own internal evidence. So also fruit may be understood as not being purified, either when it is so impure as to be difficult to purify, or when it requires no purification, but is bright, and clear, and pure of itself.