In Jaakko Hintikka's work in logic and philosophy of logic, constituents and distributive normal forms have played a very central role. This role is best understood by considering the notion of constituent in connection with other related notions and ideas. Therefore, the aim of this paper is threefold. First, we attempt to present the syntactic structure of constituents in first order (elementary) logic and to prove the existence of distributive normal forms in a technically simple, precise, and detailed way. Nevertheless, since constituents are syntactically somewhat complicated things, it is hardly possible to learn their structure in such an easy way as by merely looking at definitions and examples. Thus, one has to make some personal efforts, so to speak, with a pencil and piece of paper.