In mathematics, semantics, and philosophy of language, the principle of compositionality is the principle that the meaning of a complex expression is determined by the meanings of its constituent expressions and the rules used to combine them. This principle is also called Frege's principle, because Gottlob Frege is widely credited for the first modern formulation of it. However, the idea appears already among Indian philosophers of grammar such as Yaska, and also in Plato's work such as in Theaetetus. Besides, the principle was never explicitly stated by Frege, and it was arguably already assumed by Boole decades before Frege’s work.