Martin Heidegger is one of those thinkers who attempts to reflect on that which is (being) in a phenomenological way. That which is (being) should manifest itself as it is. In so doing, Heidegger does not remain isolated in his own world, instead he consults ideas from past ages as articulated in philosophy, that is, in metaphysics. He reflects upon metaphysics by «destroying» it in the sense that he fathoms its roots. He is convinced thereby that, in its historical walk, metaphysics has become increasingly estranged from its Greek beginnings, it has forgotten the true nature of being and is now lost in reflection upon the being. In the modern era this deviation has resulted in the absolutization of man as the subject to whom all things have become mere objects of cognition and activity. This manner of thinking has lead to the absolutization of reason, and at the same time to a failure to perceive emotion and mood, temporality and finiteness in understanding the human being. Truth is thus seen exclusively as the correspondence between the mind (judgement) and matter. Since the nature of matter is determined by the mind itself, the mind revolves in a circle and does not permit that which is to actually be what it is. Finally, intellectual reflection has mutated into cognitive-theoretical constructions and into the absolutization of subjectivistic objectivization at the expense of the ever-present possibility of expressing differently the real truth of being. Therefore it sometimes seems that such logical-philosophical rationalism exhausts itself in investigating how long a fish is able to live on dry land. Consequently, it does not seem absurd to ask oneself whether «rationality» might yet be irrational (irrational in the sense of an ideological absolutization of the rational).