Yet it is difficult to determine even the distinction between man and animal. Of course, it is easy to say that one is a rational living being, while the other is a non-rational living being. But the question is precisely this: what does reason, or the lack of reason, actually mean here? Even if we succeed in clarifying this question, it is still uncertain whether this distinction does in fact represent what is most essential and what is metaphysically important here. When we ask this question concerning the relation between man and animal, we cannot therefore be concerned with deciding whether or not man is descended from the ape. For we cannot begin to pose this question, let alone answer it, until we clearly appreciate what the distinction between them is and how this distinction should be drawn. And this does not mean finding out how humans and animals are distinguished from one another in this or that particular respect. It means finding out what constitutes the essence of the animality of the animal and the essence of the humanity of man and through what sort of questions we can hope to pinpoint the essence of such beings at all. Then again, we can only determine the animality of the animal if we are clear about what constitutes the living character of a living being, as distinct from the non-living being which does not even have the possibility of dying. A stone cannot be dead because it is never alive.
Yet the difficulty here is not merely one of content with respect to what life as such is but is equally and almost more emphatically a methodological one: by what path can and should we gain access to the living character of the living being in its essence? In what way should life, the animality of the animal, and the plant-character of the plant be made accessible to us? It is not sufficient merely to provide a morphological description of the animal's form, its limbs, and so on; it is insufficient to explore the physiological processes and then to add on some form of animal psychology. For in all of this we have already presupposed that the animal is alive, that in its behavior the animal is also disposed in a certain manner. How are we to get to the bottom of this? The animal can perhaps neither observe itself, nor communicate any such observations to us. And even if the animal expresses itself and announces itself, as it seems to us, in a variety of expressive sounds and movements, it is we who must first interpret and analyze such forms of expression.
We are thus confronted by two fundamental difficulties: [1.] What are we to determine the essence of life in general as? [2.] How are living beings as such-the animality of the animal and the plant-character of the plant---originarily accessible? Or is there no possibility of any original access here at all? But what would that imply with respect to the essential character of living beings, however this character is given? In the course of our comparative considerations both of these questions must be left open, but that also means that we must always have some answer ready, however provisional and tentative, in order to guide us as we pursue our comparative considerations. On the other hand, these comparative considerations