Morphosyntactic marking connected with the Middle contexts, broadly speaking expressing the involvement and affectedness of the subject (Cotticelli Kurras and Rizza 2013, Inglese 2020), tends to give rise to characteristic Voice syncretism, i.e., the appearance of different readings, e.g., inherently reflexive, anticausatives, antipassive, etc., which are argued to occur via allosemy at LF (Arad 2003, 2005; Marantz 2013a, 2013b; Wood 2015, 2016; Wood and Marantz 2017; Oikonomou and Alexiadou 2022).1 Looking at reflexiva tantum (RT), i.e., predicates with reflexive clitic się (SE) without any non-się marked counterparts, this paper claims that in a language like Polish, where the Middle readings are not expressed by non-active/mediopassive synthetic morphology, this class of contexts does not have to be related to one specification of the Voice, but since it depends on the reflexive SE-clitic, the syntax of the Middle encompasses all the contexts that license the insertion of this element. Only a subset of the syncretic readings in Polish arises as post-syntactic allosemy, and unergative and unaccusative SE-reflexives differ with regards to the base-generation of the nominative-marked subject. Importantly, agentive readings involve the agentive Voice with the NP argument merged in its specifier. Polish reflexiva tantum are discussed in cross-linguistic contexts of other non-alternating predicates, i.e., media tantum and deponents, and it is shown that they cover the same semantic spectrum, but differ in the syntax, especially in their active and agentive readings. It is shown that the idiosyncratic and omplex nature of reflexive tantum is reflected in its potential to create idiomatic extensions, which arise due to both overt syntax and post-spellout allosemy.