Not every organism has a brain, and not all life is organic, but everywhere there are forces that constitute microbrains, or an inorganic life of things. We can dispense with Fechner's or Conan Doyle's splendid hypothesis of a nervous system of the earth only because the force of contracting or of preserving, that is to say, of feeling appears only as a global brain in relation to the elements contracted directly and to the mode of contraction, which differ de- pending on the domain and constitute precisely irreducible varieties. But, in the final analysis, the same ultimate elements and the same withdrawn force constitute a single plane of composition bearing all the varieties of the universe. Vitalism has always had two possible interpretations: that of an Idea that acts, but is not—that acts there- fore only from the point of view of an external cerebral knowledge (from Kant to Claude Bernard); or that of a force that is but does not act—that is therefore a pure internal Awareness (from Leibniz to Ruyer). If the second interpretation seems to us to be imperative it is because the contraction that preserves is always in a state of detach- ment in relation to action or even to movement and appears as a pure contemplation without knowledge. This can be seen even in the cerebral domain par excellence of apprenticeship or the formation of habits: although everything seems to take place by active connections and progressive integrations, from one test to another, the tests or cases, the occurrences, must, as Hume showed, be contracted in a contemplating "imagination" while remaining distinct in relation to actions and to knowledge.
The plane of immanence is interleaved. When comparing particular cases it is no doubt dificult to judge whether there is a single plane or several different ones: do the pre-Socratics have the same image of thought, despite the differ- ences between Heraclitus and Parmenides? Can we speak of a plane of immanence or image of so-called classical thought that continues from Plato to Descartes? It is not just the planes that vary but the way in which they are distributed. Are there more-or-less close or distant points of view that would make it possible to group different layers over a fairly long period or, on the contrary, to separate layers on what seemed to be a common plane? Where, apart from the absolute horizon, would these points of view come from? Can we be satisfied here with a historicism, or with a generalized relativism? In all these respects, the question of the one or the multiple once again becomes the most important one, introducing itself into the plane. In the end, does not every great philosopher lay out a new plane of introduce a new substance of being ....
