The Japanese causative verb is formed by attaching the causative morpheme -sase to a verb: tabe-sase (eat-caus) ‘make eat, feed’, ik-(s)ase (go-caus) ‘make go, let go’; the initial s drops if the verb stem ends in a consonant. In the 1980s and 1990s, fi erce debate arose about the exact nature of the causative form. Should it be analyzed as being formed in syntax, or does it belong to the lexicon where it is formed by some process of word formation? One piece of evidence in favor of the “lexical” analysis was the phenomenon of blocking, in which synthetic (monomorphemic) verbs were shown to block V-sase verbs from taking on a particular meaning (see Chapter 7). Given the standard assumption that synthetic verbs belong to the lexicon, the fact that they interact with the V-sase causative verb gave credence to the notion that the V-sase causative verb also belongs to the lexicon. In the last ten years or so, a similar debate has taken place over the analysis of certain infl ectional and derivational forms in English (past, perfect, comparative, etc.) and other Indo-European languages, with blocking playing a central role (see, e.g., Embick and Noyer 2001; Embick 2007; Embick and Marantz 2008; Kiparsky 2005; Stump 2001). In this chapter, I will review the original arguments for blocking in Japanese causatives, then explore a recent proposal to analyze both the synthetic (lexical-causative) and the analytical V-sase verbs syntactically. I will then look at implications of this analysis for the acquisition of Japanese causatives and for the analysis of English causatives. I will end with a discussion on the nature of blocking, concluding that we don’t need the fi lter-based approach advocated by Kiparsky (2005) and McCawley (1978).