The beginning of pure philosophy, i.e. of pure logic, is the subject-matter of the first question of philosophy. On this question, David Gray Carlson writes the following in his "The Antepenultimacy in Hegel's Science of Logic":
On the same issue, Hegel writes in the third Remark in the Being chapter of the Science of Logic:Pure being and nothing is never before us as a thought because it is unthinkable. It is a failed thought. It is retroactively theorized only. And in support of this interpretation, it may be noted that Hegel states that pure being and pure nothing "have no separate subsistence of their own but are only in becoming."Hegel states that the beginning can be either mediated or unmediated -- but either way of beginning is refuted in advance. In other words, the beginning must fail. If it did not, then there would be no possibility of progress beyond the beginning. "Hence the advance is not a kind of superfluity; this it would be if that with which the beginning is made were in truth already the absolute." In short, it is the very nature of a beginning that it must fail; otherwise it would be result-not beginning.[P]ure being and pure nothing are not even moments. Rather, they are retrospective reflections on what must have been.[B]eing and nothing are unthinkable. As we cannot think them, there is little use in observing that they do not imply becoming.How does becoming emerge from pure being? It does not emerge at all. Becoming is absolute knowing itself, as it stands back from its own failed proposition, learning from its failure that when it tries to think an immediate thought, it ceases to be in that thought and is alienated from its product.
[N]owhere on heaven or on earth is there anything which does not contain both being and nothing in itself. ... All further logical determinations ... (existence, quality, and in general all the concepts of philosophy) are therefore examples of this unity.
These passages resonate with a related idea of Collingwood's in An Essay on Metaphysics:
An ordinary science is the science of some definite subject-matter, having special problems of its own that arise out of the special peculiarities of the subject-matter, and special methods of its own that arise out of the special problems; whereas the 'science of pure being' has a subject-matter which is not a something but a nothing, a subject-matter which has no special peculiarities and therefore gives rise to no special problems and no special methods. This is only a roundabout way of saying that there can be no such science. There is not even a quasi-science of pure being: not even a thing which in certain ways resembles an ordinary science and in certain ways differs from it, such as a collection of statements that are not certain but only probable, connected together in ways that are not convincing but suggestive. There is no even a pseudo-science of pure being: not even a collection of what seem to be statements but are in fact only the record of guesses, intellectual gropings or emotional reactions that take place within us when we confront an object we do not understand.This is a more than twice-told tale. ... It is all implied in what Hegel said when he expanded that phrase of Kant's into the more explicit statement that pure being is the same as nothing. I quote these precedents ... because I wish to remind [the reader] that what has been said [here] is nothing new, but has been a commonplace for over two hundred years.I propose to call the science of pure being, when I want a one-word name for it, ontology. ... Ontology will be my name for a mistake which people have made, Aristotle first and foremost, about metaphysics.
Collingwood also writes in his lecture manuscript "The Nature of Metaphysical Study":
Just as the idea of pure being cannot be grasped in its bare abstraction, without allowing it to sprout determinations out of itself like nothing and becoming, so the idea of metaphysics in general cannot be grasped in abstraction by a purely formal definition, unless we will allow this abstract idea to sprout determinations of its own in the shape of particular metaphysical problems and doctrines. These are not mere instances of metaphysical inquiry ... [but] are universal and permanent problems and theorems of all metaphysical thought, and you will find that all metaphysicians have at all times and in all places concerned themselves with these ideas, the ideas of being, of nothing, and of becoming, as problems arising necessarily out of the very nature of metaphysical thought.... I have tried to expound the idea of metaphysical inquiry as an inquiry always concerned with the same fundamental problems: being, nothing, becoming, and of course others necessarily arising out of these and their interrelation.
Even Heidegger, the great exponent of "ontology," admits the same point with regard to the problem of thinking pure being. He writes in Division II of Being and Time:
The existential interpretation of the historicity of Dasein constantly gets caught up unexpectedly in shadows. The obscurities are all the more difficult to dispel when the possible dimensions of appropriate questioning are not disentangled and when everything is haunted by the enigma of being [emphasis is in the original text] and, as has now become clear, of movement. Nevertheless, we may venture an outline of the ontological genesis of historiography as a science in terms of the historicity of Dasein. It should serve as a preparation for the clarification for the task of a historical destruction [Destruktion] of the history of philosophy to be carried out in what follows.
Heidegger admits the "obscurities" which arise out of the "enigma of being," and he does not go any further here in clearing such obscurities. With the apologetic word "Nevertheless," Heidegger, in his characteristic style, pushes on with his "destruction" -- and here it is important to connect this to Derrida's deconstruction as well, and to read the method of deconstruction as one of inheriting this Heideggerian attitude towards the "enigma of being." However, being may perhaps appear enigmatic to us because it is also enigmatic in itself; there is nothing to think about in pure being. To call this nothingness an "enigma" seems to be an act of investment, of positing determinations into this nothingness in order to later make them "explicit." If being is confronted with in its pure simplicity, and if nothing is what one encounters as a result, then this result should be taken literally and at face value. This is the way to dispel the enigma of being. Otherwise, metaphysics becomes hermeneutical in the bad sense of the term, and philosophy becomes aesthetic philosophy, a philosophy based on feeling and on free play, fueled with the rhetoric of investment and explication; a mere "love of knowledge," not actual knowledge.
In An Essay on Metaphysics, Collingwood calls for a "metaphysics without ontology," and this seems to be exactly what Kant and Hegel are trying to do in their Critique of Pure Reason and Science of Logic. The name for this metaphysics may also be transcendental philosophy, critique, logic, pure logic, and so on.
The reason why metaphysics is so deeply concerned with its starting-point or beginning, and the reason why it always comes back to the idea of pure being and, in its failure to think this idea on its own, "sprouts" the determinations of its own thinking -- the reason for this is, namely, that philosophy is interested in what is, or in what is categorically true. This is why (1) philosophy cannot begin from ready-made presuppositions, and (2) philosophy first turns to the question of the meaning of being. Ready-made presuppositions still contain a categorical element, and the meaning of being cannot be stated plainly or once and for all. Metaphysics disentangles the categorical element from such pre-suppositions and shows in what way one can and does state the meaning of being.