Philosophy is nothing other than the knowledge of the eternal or the speculative Idea, reason, or truth; these different expressions all designate the same substance. Philosophy presents the Idea as the only cause. Consequently, in all finite effects philosophy sees nothing but the Idea. But, one objects, "there are so many philosophies; the one system contradicts and negates the other; in which of all these can one find the truth?" To this one can answer that the different philosophical systems - assuming that they really are philosophical, i.e., that they are penetrated by the speculative Idea, for otherwise they cannot be considered - all contain the same philosophy, only seen from different levels of culture in the development of humanity, just as the different religions all contain the same God, viewed from different standpoints in the religious Idea, and just as the different works of art contain the same beauty in changing forms, or the different forms of poetry contain the same poetry under different conditions. All differences are grounded in unity; they are only moments in it, i.e. they are the necessary stages in the unity's own development. The truth is not so empty or abstract that it could not, without damage to itself, take up the conflicting moments and keep them in the common womb. They contradict, they sublate each other; for just this reason it is absurd to ask: "in which of them is the truth?" It is in none of them, but they are all in it.
Every age, which is not in a critical transition but which finds itself in a calm and orderly condition, has its philosophy, which is the result of all the previous experience and of the knowledge to which that experience has led. It is important to note that philosophy cannot appear before there is material for it to take possession of, just as, in the order of nature, a child cannot be born before the nourishment for it has been prepared in the mother's breast. Indeed, philosophy, as knowledge of the eternal Idea, transcends all temporal change; but every determinate or individual philosophy comes on the scene in the given age and is tied to the conditions of that age. Its material therefore does not lie in the future, which neither is nor has been; it is not prophetic and cannot, indeed, does not want to be. Likewise, the material cannot be sought in the present, because the present is not yet finished and therefore partly falls inside the limits of the future; if it were finished or completed, then it would belong to the past. Only the past is a finished and thus an actual material; but by taking possession of the past, philosophy makes it something present, since it indeed expresses the highest and deepest thought about it by humanity at that time. Thus, philosophy brings about the resurrection of the dead to life. Hegel says, most aptly, that only when a form of life has become old does philosophy come forth to it: "The Owl of Minerva spreads its wings only with the falling of dusk." (Philosophie des Rechts, p. xxiv. 1821, Elements of the Philosophy of Right)
... What is substantial in philosophy is the Idea, truth and reason; but philosophers do not create the Idea, truth and reason. The change is in the different forms under which the unchangeable substance is presented, that is, the different philosophical systems; but each of these is a product of its age, an individual, to which the present has given birth into the world, but whose genealogical table reaches back through the entire past. …