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Information structure divides sentences into topic (given context) and focus (new, salient information), affecting both semantics and prosody. Topic-fronting, focus movement, and contrastive stress are syntactic and phonological reflexes that signal information packaging.
Identify topic and focus using diagnostic tests (congruence with questions, contrastive stress, word order); study how languages vary in marking information structure (intonation vs. word order).
Information structure is not purely pragmatic; it has grammatical reflexes (word order, movement, agreement effects in some languages) and semantic consequences.
From your study of discourse analysis, you know that sentences don't occur in isolation — they participate in a larger discourse context that shapes how they are interpreted. From formal pragmatics, you understand how context and speaker meaning interact with the literal truth-conditional content of an utterance. Information structure sits at the intersection of these: it is the internal organization of a sentence that packages information relative to what has already been established in the discourse. Two sentences can have identical truth conditions but very different information structure — and choosing the wrong one in context sounds infelicitous, awkward, or misleading even if technically true.
The foundational distinction is between topic (what the sentence is *about* — the entity or state of affairs already under discussion, the given information) and focus (what is being *said about* the topic — the new, salient, or asserted information). In "Sarah won the prize" (with stress on *Sarah*), *winning the prize* is the topic (already in discussion) and *Sarah* is the focus (new information identifying who). In "Sarah won the prize" (stress on *won*), Sarah might be the topic and the winning is new. In "Sarah won the prize" (stress on *prize*), the prize contrasts with something else. Prosodic stress is the clearest diagnostic in English, but the topic-focus distinction is present across languages and realized in very different ways.
A useful diagnostic tool is the question test: focus is the part of a sentence that constitutes a felicitous answer to a congruent question. If someone asks "Who won the prize?", the answer "Sarah won the prize" is congruent — *Sarah* is the focus because it provides the new information the question requested. The answer "Sarah WON the prize" would be infelicitous: it focuses on the winning rather than the winner, and is not a natural response to that question. This test reveals that information structure is not just a speaker's stylistic choice but a grammatical feature of sentences that must match discourse context to be appropriate. Mismatches produce presupposition failure or pragmatic oddness: saying "It was SARAH who won" in response to "Did Sarah win?" presupposes that someone was being inquired about, which is a mismatch.
Languages differ substantially in how they grammaticalize information structure. English uses prosody (nuclear stress placement) and cleft constructions ("It was Sarah who won"). Many languages use word order systematically — in Czech and other Slavic languages, old information tends toward the front of the sentence, new information toward the end, regardless of grammatical subject-object relations. Some languages use morphological focus markers — in Somali and many African languages, a particle or verbal agreement marking signals that the accompanying constituent is focal. In Japanese, the topic particle *wa* explicitly marks the sentence topic. These cross-linguistic patterns suggest that information structure is not merely a pragmatic add-on but a grammatical category that languages encode with varying grammatical machinery.
The theoretical significance is that information structure is neither purely semantic (it doesn't change truth conditions in most cases) nor purely pragmatic (it has grammatical reflexes in syntax and morphology). It sits at the interface — which makes it difficult to localize in a modular theory of grammar and productive for studying how syntax, semantics, and pragmatics interact. Sentence topics create accessibility for subsequent reference: once Sarah is established as the topic, later pronouns can refer back to her without disambiguation. Focus creates contrast sets implicitly: stressing "Sarah" implicates that other candidates existed. These are not mere stylistic choices but structural features that constrain how discourse coheres.