Full Idea
The art of finding intermediate terms (the 'middle term') is the art of 'analysis'.
Clarification
The middle term is the linking concept in a syllogism
Gist of Idea
Analysis is the art of finding the middle term
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 4.02)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.369
A Reaction
This proposal is straight out of Aristotle's 'Posterior Analytics'. Nowadays we would say there was much more to analysis, the finding of necessary and sufficient conditions being the most obvious way of putting it.