Heidegger’s philosophy is the philosophy of Being, a notion he accuses philosophers before him of having obscured and pushed into foggottenness. Since for him being and truth are identical, we can rightly call his philosophy of truth. His ontology as outlined in Sein und Zeit emphasizes the importance of understanding the nature of one who asks the question of Being, in order to be able to penetrate the nature of Being. For Heidegger the study of what makes human beings what they are, or the study of what each of us is Dasein is the door for reaching the understanding of being. According to Martin Heidegger therefore Ontology is the hermeneutics of Facticity. It is by understanding what facticity means that we can grasp what Heidegger proposes to us as his ontology. “The concept of “facticity” implies that an entity “within –the- world” has Being – in-the- world in such a way that it can understand itself as bound up in its “Destin” with the Being of those entities which it encounters within its own world. “ here one has to understand what Heidegger means by two terms, which he connects to make the expression “Being –in-the - world” Here one has to understand what Heidegger means by two terms, which he connects to make the expression “Being –in-the-world” ( in-der-Weld-sein) “being- in “ and “world”. “Being –in” means “to reisde alongside…” in the meaning of “being familiar with …” “world “- …….. menas “the how “ (condition, state) of being and not the being itseld. This “how” is the way in which Dasein comports itself in relation to other beings that are not of the nature of Dasein-a relation of being aware and understanding, which is what Heidegger calls Beings –in the- world or transcendence. Facticity in this meaning therefore is the comportment of Dasein, which differentiates it from other entities, and hence it is called existential to differentiate it from categories, which are traits of entities different from Dasein. “Being-in”-world as its essential state.” Daseing therefore is familiar with the environment in which it lives and is aware of things it encounters, or in other worlds, Dasein has a world, hence encounters other beings giving them meaning and defining them in the process. Other entities (which Heidegger calls entities present-at-hand), which are “worldless” in themselves…. Can never touch each other, nor can either of them “be alongside the other.” Thus Heidegger shows how Dasein behaves in relation to other entities, which is encounters giving them meaning. The special character which enables Dasein to encounter other entities is that of care (sorge) Care is proposed as a replacement of the traditional understanding of man as a spiritual being located in space because of its bodily nature. Apart from expressing this view as naïve Heidegger does not tell us why an is not a spiritual being located inspace by its bodily nature. Neither does he tell us what comes of the obvious spiritual – body nature of man. For Heidegger Dasein is identified through its activities, such as: Having to do with something, producing something, attending to something and looking after it, making use of something, giving something up and letting it go, undertaking, accomplish, evincing, interrogating, considering, discussing, determining ….. all these ways of Being- in have concern as their kind of being. Hence Heidegger’s human being is defined by what proceeds from his actions, not what he really himself. Putting activity as the definition of human being makes it difficult to include in human group, not only bodily and intellectually disabled people, but also children, disabled persons, very old people as well as anyone may define as inactive, depending on the meaning one gives to activity and productivity. It is true that care makes part of human existence, but it is not the definng factor of human beings. Rejection of Aristotelian definition of man as ……………….and insisting that this “never meant “rationality”, but talking speech; hence man is a being which has its world in type of the spoken.” Which this Heidegger also sidelines the importance of Aristotelian- thomistic basic principles of reality, namely, the principles of non- contradiction, principle of identity, principle of excluding the middle, principle of analogy, participation and that of sufficient reason. These are principles, which necessarily accompany any understanding of reality and which are discovered, not made, by human intellect. This oversight comes up also when Heidegger makes Being and time identical, or rather when replaces Being with time. His interpretation of these two key Greek words,………. And ………. And ……… as to mean speech and time ontology and differentiates him from what he constantly calls “tradional philosophy”. The concept of substance, as that which persists in existence and remains intact through changes or motions, as treated in the seventh book of metaphysics of Aristotle, eludes heidgger completely and with it the world outside human consciousness. the ability to speack is the assence of Dasein and ontology becomes the analysis of Dasein’s states of mind or moods (Befinlichkeiten) Since Heidegger does not want to see the notion of substance, he cannot follow the reasoning of Christian philosophy of St. Thomas Aquinas in putting God as the absolute subsistent Being at the origin of reality. As long as the principle of causality remains meaningless to him, Hiedgger can only see the talk of Christian philosophy as a reference to “Wooden iron”. His definition of metaphysics as the subject where the question “why is there at all something rather than nothing?” becomes a very important question but in a misplace context. this question cannot be asked, neither can there be any attempt to answer it if we remain in the subject asking the question and pay no attention to principles that lead to possibility of replying to this basic question. In ontology without the concept of substance the “something” is not there; hence the question itself cannot begin to be asked. It is in this understanding of man and reality Heidegger situates his concept of truth. Since Dasein is a special kind of monad – mundus concentrates, with neither inside nor outside, Heidegger cannot but localize truth into Dasein. Having rejected the need to prove the existence of the world external to Dasein, Heidegger cannot but define every reality departing from Dasein. And since Heidegger’s ontology has no regard to first principles, like that of causality and non-contradiction, he proposes a mysterious nihil originarium as the foundation of everything that exists. Section 43 of Sein und Zeit makes us rightly suspects that, Heidegger losses the concept of substance and the world external to man, and proposes time and Dasein as the only reality that remains. This makes us ask some questions about the results of this omission. With Aristotle’s understanding that every understanding must of something, (every symbol)) we cannot see Heidegger’s suggestion of analytical of dasein as ontology being a valid philosophical proceedings. The concept of substance, in the sense of what persists in all charges, with all principles that accompany the concept of substance, are absent completely Heidegger’s ontology. Time, which replaces substance also is subjected to dependence on dasein, hence enclosing the whole reality into the understanding of doorless and windowless dasein. But we cannot talk of change or existence without talking about that on which change happens or what persists in existence dispite all changes, just as Aristotle states: However true it may be that all generation and destruction proceed from someone or more elements, why does this happen and what is the cause? For at least the substratum itself does not make itself change; … men were again forced by the truth itself, … to inquire into the next kind of cause … when one man said, then, that reason was present-as in animals, so throughout nature-as the cause of the world and all of its order, he seemed like a sober man in contrast with the random talk of his predecessors For this reason Aristotle considers metaphysics to be the study of causes of reality and principles of change or motion. By identifying Being and time and locating them into Dasein, Heidegger looses trace of the outside world and cannot explain the fact that every knowledge is intentional. In the heideggerian ontology (symbol), in the meaning of speech dominates (symbol) (substance) and hence ontology becomes the analysis of Dasein’s ability to speak, in Aristotelian without paying attention to what is spoken about substance, in Aristotelian meaning of what persists in existence. This is an ontology which we name in this work as existential solipsism, following Heidegger’s insistence that there exists no world outside Dasein. Heidegger’s rejection of the need for the proofs of the outside world, and his definition of Dasein as monad having neither outside nor inside, justifies our charge, can be grasped only by the intellect and functions as reference for any knowledge. The way intellect graspes reality is outlined in the above mentioned principles of reality. This reference of the intellect is what Aristotle calls the “what”, and puts as the foundation of his Metaphysics, as he tells us: While Being has all these senses, obviously that which is primarily is the “what”, which indicates the substance of thing…. Now these are seen to be more real because t here is something definite which underlies them; and this si the substance or individual, which is implied in such a predicate; for “good” or “sitting” are not used without this. It is because of neglect of the concept of substance that we find Heidegger ignoring also concepts that make clear the different modes of Being of substance. Among the most important concept ignored by Heidegger with devastating outcomes are the concepts of analogy and participation. Without the concept of analogy it is difficult to talk of the ontological differences; the difference between Being and beings. Heidegger’s talk of artistic objects being more real than natural things is another result of mixing up Plato’s concept of participation. We can talk of the ontological difference only when we have some beings, or at least one being, that possesses Being in full or in higher degree than others. Because of lack of clear understanding of the concept of analogy Hiedegger does not accept traditional definition of a human being as an individual substance of rational nature. Also the word oʋσία is taken equivocally to mean time and Being, recover the concept of time, but lose the concept of substance, and hence find it difficult to talk of the world outside of Dasein. In the Hedeggerian analysis of Dasein transcendent attributes, which are traditionally attributes of Being, are located into Dasein and termed freedom. The notion of freedom is also understood as something enclosed into Dasein’s individualism. St. Thomas’ concept of freedom as freedom of exercise and freedom of determination of human acts would be a foregn concept in the Heideggerian ontology. It is because of the not well understood nature of man that Heidegger finds himself identifying his ontology of Dasein with the political movement of the National Socialim of Adolf Hitler. This inadequate definition of human beings as beings living in an instrumental world, existing only to realize what benefits them, is what we also find in William James pragmatism as well as the today’s political economic talk of globalization. In this kind of thought truth becomes identical with usefulness and the profitableness. All attention is payed to the end without regard to means used to achieve the end. Justice becomes the wish of the strong ; international law becomes binding only to the poor and serves the interest of the rich individuals or nations. In short what one achieves, not what one is , defines his nature. It is only when we accept that a human being is an individual substance of a rational nature, that we rediscover moral values, see the meaning of social justice, be it in business or in the so-called international law. Here truth becomes an ideal reference recognizable by everyone with the human nature, that is, with rationality. Under this understanding, the world market where the same nations decide the value of money, arrange selling and buying prices of articles will show its unjust face clearly. Here truth becomes an independent concept, having things themselves as reference and discovered by the intellect. This needs a bipolar reality with human intellect and the entities outside the intellect intactly existing, without reducing one to the other as Heidegger attempts. The correctly understood nature of human being leads to correct concept of reality. Ontology cannot in any way be only the analysis of Dasein, if Dasein is also to be taken as one of entities to be understood.