AbstractThis article is mostly devoted to a critical review of the main analyses of root infinitives. Confronting these analyses to acquisition data from French, it is shown that an analysis in terms of a “null auxiliary” is more compatible with the data than the alternative hypotheses. However, an analysis in terms of a null or deleted auxiliary raises some difficult questions with respect to the existence and the nature of null elements in child language. Rather than appealing to null or deleted elements, it seems more appropriate to assume that children utterances do not include an auxiliary or a modal and that the corresponding node is simply not projected. An analysis along these lines is developed in the last section of the article.