 So far Brentano’s theory seems to have a sound footing. Now we need to make a big step when we consider Brentano’s most radical thesis: what we called his reduction thesis (see  section 1, claim 6):  “The reducibility of categorical propositions, indeed the reducibility of all propositions which express a judgement, to existential propositions is therefore indubitable” (PES 218 [II 60; SVS 1, 239). Before we can ask on what basis Brentano makes this claim, we need to get clear about its meaning.