John Stuart Mill Quote

An hypothesis being a mere supposition, there are no other limits to hypotheses than those of the human imagination; we may, if we please, imagine, by way of accounting for an effect, some cause of a kind utterly unknown, and acting according to a law altogether fictitious.

A System of Logic, Ratiocinative and Inductive, Book III, Chapter XIV (p. 290), Harper & Brothers Publishers. 1867