Formal typology catalogs systematic cross-linguistic variation and explains it through formal constraints and parameters. Languages cluster by word order, case systems, and argument marking, yet all languages encode agency, tense, and aspect. Formal analysis reveals deep structural similarities beneath surface diversity: constraints permit only certain features to co-occur, limiting the space of possible human languages.
From your prerequisite work in linguistic typology, you already know that languages vary enormously on the surface — different word orders, different sounds, different ways of marking tense and possession — and yet these variations are not random. Certain patterns appear universally or near-universally; others are strongly correlated. Formal linguistic typology moves beyond cataloging these patterns to explaining them: why do languages cluster in the ways they do, and what principled constraints rule out the patterns that never appear?
The central concept is the parameter — a binary or small-scale formal choice in a language's grammar that, when set one way or another, predicts a cluster of downstream properties. The classic example is the head-directionality parameter: languages consistently place grammatical heads (verbs, prepositions, nouns) either before their complements (head-initial: English, French) or after them (head-final: Japanese, Turkish). This single setting cascades through the grammar: head-initial languages tend to have prepositions and SVO or VSO word order; head-final languages tend to have postpositions and SOV word order. You don't observe random mixtures of these properties because the parameter links them formally. The Principles and Parameters framework, which you'll study next, builds this insight into a generative theory of cross-linguistic variation.
The complementary concept is the typological implicational universal — a constraint of the form "if a language has property X, it also has property Y." Greenberg observed that if a language has VSO order, it almost invariably has prepositions rather than postpositions. If a language has both nominative-accusative and ergative-absolutive patterns, the ergative pattern applies to transitive perfectives while the nominative pattern applies elsewhere (split ergativity). These universals constrain the typological space — the set of logically possible language types. Formal typology is the project of explaining why the actual space of human languages is so much smaller than the logical space: what formal principles rule out the attested impossibilities?
The practical payoff is a more principled view of language acquisition and change. If grammars are governed by formal parameters, then acquiring a first language can be modeled as parameter-setting — a child hears enough input to fix the head-directionality parameter, and a cluster of other grammatical properties falls into place automatically. Language change, by this view, can occur when a parameter gradually shifts as speakers reanalyze input. This formal apparatus turns descriptive typology into a testable theory: the distribution of cross-linguistic variation becomes evidence for or against specific formal proposals about what the parameters actually are.
Formal typology also sharpens the distinction between deep structure and surface form. Two languages with radically different surface appearance — an SOV language with postpositions and an SVO language with prepositions — may share the same underlying formal architecture instantiated with different parameter settings. Conversely, two languages with similar-looking word orders may achieve them by entirely different formal mechanisms. This is the insight that makes formal typology more than an empirical catalog: it is a window into the abstract architecture that all human grammars share.