In Plato, the concepts and the forms of relationship between the concepts that correspond to genera and species imply realities that transcend the world of existence, rather than hollow categories. Aristotle is the first person that comes to mind when it comes to the problem of genus-species relations. However, Plato and Aristotle have opposing views. While Aristotle considers the general concepts corresponding to genera and species to be the hollow abstractions of the mind, Plato thinks that these correspond to the purest realities. In line with this understanding, Plato does not deal with the truth and inaccuracy of inter-conceptual relations within the positive and negative propositions drawing from concrete reality relations but rather based on relations among the forms themselves, which he accepts as pure realities.  In our article in which we will discuss the negative propositions and the problem of nothingness in Plato, for sake of a clear explanation of the problem, we will explain the development of Plato's concept of "Form" in the sense of genus/species, his criticism directed towards Protagoras' theory of perception to open a space for the transcendence of the forms, his theory of "partaking" among the forms, and what he understands with the dialectics which is the method of thinking all these problems; in this way, we will discuss –as the main problem of the article- the explanations on the concepts of Being and Nothingness made by him within the context of positive-negative propositions which arise from the relations among the absolute forms, or -using the terms of Plato- "summa genera".