Semantic Syntax (SeSyn) is the theory of algorithmically formalised grammars generating the well-formed sentences of a language L from the corresponding semantic input. Though it began as an off-shoot of Chomskyan transformational generativism (ChTG) called Generative Semantics, it differs radically from ChTG in that (i) the input of the grammar is the semantic analysis (SA) of a sen-tence S, (ii) the SA of S is formulated in a specific language of incremental predicate logic with quan-tifying and qualifying operators (including the truth functions). Unlike a ChTG grammar, which is an algorithm triggered by an arbitrary initial symbol, a SeSyn grammar is triggered by a seman-tically well-defined input structure, originating in cognition. SeSyn thus makes explicit how pro-positional thoughts are expressed in any given L, having been generated by, or in, cognition and cast into the predicate-logical propositional form of an SA, combined with a speech-act operator. SAs are not universal but already geared to the L at hand through the choice of language-specific lexical predicates, which dictate the predicate-argument struture of the sentences of L. SeSyn is thus unequivocally mentalist-realist, in that it actively strives for integration with cog-nitive (neuro-)science, even though the gap between mental systems, structures and processes on the one hand and their neural correlates on the other has not (yet) been bridged. ChTG has always—due to its neopositivist (Carnapian) origin as an algorithm triggered by an arbitrary initial symbol—been ambiguous in this respect. ChTG is firmly rooted in mid-20th-century neoposi-tivism and cannot be taken to be part of the ‘cognitive revolution’ of the 1960s, despite claims and appearances to the contrary. It is caught between the cognitive absurdity of its formalism and the formal deviousness of its sometimes professed realism. The semantics of SeSyn is likewise unambiguously cognitive-realist, taking the notion of mental proposition as basic to cognitive, logi-cal and (con)textual processing. SeSyn thus requires sweeping and highly consequential measures with regard to standard predicate logic, which current model-theoretic semantics has been unwilling to take, thus making itself irrelevant to the study of natural language. SeSyn is thus any-thing but just another theory of grammar: it manifests a thoroughly new, mentalist, anti-positivist approach to linguistics, cutting through the horror mentis that has plagued the human sciences for over a century. (This, incidentally, would help explain the fierce hostility from ChTG circles SeSyn has consistently been faced with ever since its first beginnings in the 1960s.)

The mentalist-realist approach of SeSyn has proved to be empirically superior to any existing alternative. This assertion cannot be seriously underpinned in a 45-minute talk but it can be dem-onstrated by a few examples. Three such examples will be presented: (i) Verb-Clustering through the rule of Predicate Raising, (ii) Auxiliation, and (iii) the treatment of quantifiers (which turn out to be grammatically similar to prepositions). For all three it will be shown how SA-input tree struc-tures are algorithmically transformed into surface-structure output tree structures of a number of different languages. It will become clear that these processes are found in indigenous languages all over the world, given well-defined language-specific boundaries, which makes SeSyn partic-ularly relevant for linguistic typology, which now ranks as the most promising branch of linguis-tics but has so far conspicuously lacked an adequate theoretical basis.