 Propositional quantification made an early appearance in Lewis, Langford, &amp; Lamprecht 1932, which is commonly acknowledged to have pioneered the study of modal logic. They outlined a formal system of modal logic with propositional quantification, which they used to formulate an Existence Postulate designed to guarantee the existence of at least two propositions that are consistent and independent from each other. (This is postulate B9 in the entry on the  modern origins of modal logic.)  They used the postulate to make sure strict implication did not collapse into material  implication.[16]