 Gottlob Frege  showed how to resolve these difficulties for classical logic in one fell swoop. His system of logic, published in 1879 and still in use (with notational modifications), was arguably the single greatest contribution to the subject. So it is significant that on Frege’s view, propositions do not have subject-predicate form. Indeed, his leading idea was that propositions have “function-argument” structure. Frege thereby drew a substantial distinction between logical form and grammatical form as traditionally conceived. This had a major impact on subsequent discussions of thought and its relation to language. Though before turning to details, it is worth taking a slight detour to note that Frege did not think of functions as abstract objects like numbers.