CONCEPT
Compositionality
The principle, foundational in Frege's logic, that the meaning of a complex expression is fully determined by the meanings of its parts and the rules of their combination—and the most powerful available test for whether a system has genuinely learned structure or only approximated it.
You can understand a sentence you have never heard before. That capacity—to grasp an unbounded number of novel expressions from a finite stock of words and rules—is the defining feature of human language and the principle behind it is
Frege's: the meaning of a complex expression is determined by the meanings of its parts and the rules by which they are combined. Compositionality is not merely a fact about language; it is the structural guarantee behind two properties any account of mind must explain. The first is
productivity: from finitely many elements, infinitely many meanings, so that language is not a memorized list but a generative engine. The second is
systematicity: the abilities come bundled—anyone who understands “the lawyer admired the doctor” can thereby understand “the doctor admired the lawyer,” because both draw on the same compositional grasp. Systematicity is the fingerprint of genuine composition, and it is precisely