Semantics takes the structures syntax builds and asks how they relate to reality, beginning with two problems that show why this is hard. Vagueness means that the boundaries of a meaning are blurred, and polysemy means that one form can carry several related meanings, as with Bank or Flügel. Wittgenstein’s early picture theory offers a demanding ideal in response: language mirrors the world as a set of atomic facts, and whatever can be thought can be said clearly. Everyday speech falls short of it, which is why ambiguity is treated as a sign that a thought has not yet been fully clarified.
The most important structural idea is the principle of compositionality, attributed to Frege. The meaning of a complex expression is computed from the meanings of its parts and the way they are combined. It explains how speakers understand sentences they have never heard, and it ties semantics back to syntax, since changing one component or the structure changes the meaning of the whole. The semiotic triangle separates three things that are often confused, namely the sign as a form, the concept as a mental representation, and the referent as an object in the world.
This triangle leads to the central theoretical opposition. Externalism locates meaning in the world, in particulars and properties, and is criticised for ignoring individual and cultural variation and for neglecting cognitive mechanisms. Internalism locates it in mental structures, so that strictly speaking there are as many words chair as there are speakers, and it is criticised for underrating the social and historical dimension of language.
Further, we can assign semantic roles such as agent, patient, experiencer, theme and instrument, which describe what participants do or undergo in an event and connect a syntactic position to a phrase’s meaning. Word meaning and sentence structure together still leave open how meaning shifts with the situation of utterance, which is what pragmatics studies next.