“Form of life” is considered one of the most significant concepts in Wittgenstein's later philosophy. This term is one of his most ambiguous philosophical concepts. This paper tries to explain the specific and fundamental role of “form of life” as a cornerstone for the whole of Wittgenstein's later philosophy; a role that has not attracted much attention in Wittgenstein scholarship. From the author's perspective, describing the form of life as a condition for the possibility of language can put an end (...) to some of the challenges in Wittgenstein's later philosophy such as Behavioralism, being trapped in general linguistic relativity and the reduction of all reality to linguistic principles. This study attempts to prove the fundamental role of this concept by studying Wittgenstein’s later position toward philosophical explanation in general and pictorial theory of language in particular, and by analyzing in detail the concept of form of life in his later works. Finally, the authors will provide a possible fifth path entitled “Phenomenological Interpretation” through a critical analysis of the four existing interpretations on the concept of form of life. (shrink)