Full Idea
Leibniz invented the concept of 'blind thought' - reasoning by a manipulation of characters without being able to recognise what each character stands for.
Gist of Idea
'Blind thought' is reasoning without recognition of the ingredients of the reasoning
Source
report of Gottfried Leibniz (Towards a Universal Characteristic [1677]) by Richard T.W. Arthur - Leibniz
Book Reference
Arthur, Richard T.W.: 'Leibniz' [Polity 2014], p.30