What is the possibility and possible ? Yet anyone responding to this question must understand the meaning of possible being, contingent being and necessary being. In this paper we wish to discuss the analysis of modal terms especially "possible" concept. The explanation and analysis of modal terms is a matter of dispute among Ancient logicians.We are unable to define modal terms adequately. One might say that the definition of modal terms is only nominal definition. In due to the fact that there is a negative character of the definition of modal notions, we could only describe a modal concept at the level of nominal definition. Some logicians asserts that definition of modalities is really circular, because modality can only be defined with each other. There is not determinate number of modal terms among the logicians, nevertheless the standard logical modalities might be arranged as follows in Aristotle's Second Book Peri Hermeneias: possible, impossible, necessary and contingent. According to mediavel logicians these four c'oncepts are standart modalities.Megarian and Stoic philosophers held that all truths about the,world are necessary. Some of the Megarians including Diodorus held deterministic views. Diodorus formulated his deterministic views in an argument entitled "The Master Argument". Aristotle's criticism of the Megarians turns on the concept of possibility.