Frege's invention of the predicate calculus, first published in his Begriffsschrift of 1879, has been the most influential event in the history of modern logic. The predicate calculus made formal logic an object of study for many logicians and mathematicians, and consequently fundamental logical concepts were clarified and some notable logical theorems were proved. Moreover, the calculus both constituted a language which many found of philosophical significance, and was used for the analysis of natural language. Partly as a result, the philosophy of language acquired an unprecedented eminent position in philosophy. For some time, many philosophers thought that it is, or should be, what philosophy consists in; and although this position is not prevalent any longer, the importance of logic and the philosophy of language both as domains of philosophical investigations and for other philosophical studies remains undisputed.