The Commens Dictionary
Quote from ‘Short Logic: Chapter I. Of Reasoning in General’
So, cultivators of the art of reasoning found themselves long ago obliged to institute a speculative grammar which should study modes of signifying, in general. It is best regarded as separate from logic proper; for one of these days philologists may take it in hand, for which logicians will thank them.
An art of thinking ought also to recommend such forms of thinking as will most economically serve the purpose of Reason. [—] Since this is the general foundation of the art of putting propositions into effective forms, it has been called speculative rhetoric.
The sciences of speculative grammar, logic, and speculative rhetoric may be called the philosophical trivium.