The paper is based on the research conducted by Horvath and Siloni (2009), who investigated the nature of the lexicon in Modern Hebrew. The centre of their study was whether the mental lexicon has an active role in grammar, which means that operations can take place in it, or it contains just a list of entries. They focus on voice alternations to come to conclusions concerning the nature and the organization of the lexicon. What I concentrate on is whether the so called causative-anticausative alternation is represented in the lexicon, or in the syntax in Hungarian. Horvath and Siloni use idioms to prove their point that idiomaticity is stored in the lexicon at the level of words. Their findings motivate the need for my study. I compare the Hungarian and English languages, and I also try to figure out whether the conclusions of Horvath and Siloni (2009) hold also of these languages. I collected my data from 4 idiom dictionaries: Cobuild, Thesaurus, and Nagy György’s Hungarian-English and English-Hungarian Idiom Dictionaries. Besides these dictionaries, I used 2 online corpora: the British and the Hungarian National Corpora. After collecting a sufficient number of idioms, I checked their behavior with Google-search. The searches confirmed whether speakers use the particular idioms in everyday speech or not.