The modern materialism (MM) answers to the question of WHAT is a thought quite surely and unambiguously: it is a product of the brain, one of its functions. This is the very place where it appears and where it rests – at least until it is formulated and (after that) is spoken, fixed (depicted, written etc), until it is passed by material means to/into another brain which is also a material object. At that, MM limits the notion of material reality to only the physical one.
    MM puts the thought out of matter. MM, philosophy consider the "matter" as that and only that something, which is real (being, present, non-absent) independently on arbitrariness of a materialist (philosopher, explorer, observer). But a "thought" is just something arbitrary.
    However, even if it is true, so true only concerning his own (materialist's) thought. A thought of any other person doesn't depend on the explorer's arbitrariness just as well (by the same criteria) as a physical body of this "another" person. It means, a thought is also material something. As far as a thought (this kind of matter) is not of physical nature, is not а part of physical reality (of physicum ), it is inevitable to admit a thought to be a part of the metaphysical reality (of metaphysicum ).
    This work is devoted to formal/severe/"scientific" substantiation of this non-trivial idea and of several consequences, following it. The psychology, which explores psyche as a part of Nature, as a material (metaphysical) object, becomes a part of natural sciences, one of fundamental sciences.
    This idea may seem to be obvious when it is already formulated, but the author – the consistent materialist (!) – went to it not a single year (1975-86), analyzing why, how his (of a psi-technique-operator/healer) thought about his patient gives positive (desirable) changes of/in the patient's health state in those very cases when NOTHING links them (a patient and a healer), except/but this thought. It was elicited (turned out) that a thought works, gives results. And only material something can work in the material world.
   To come to the idea was not easy for it doesn't agree with severe opposition of "material" and "ideal" which is accepted by MM – either the matter is primary or the consciousness. Any third possibility is a priori excepted here. But a material thought is just something third, is consequently something that can not be. If a thought is material, so the notion of mater loses its sense for there is nothing to be opposed to it. The notion becomes identical to such universal notions as Nature and Being, becomes something that covers everything without exception.
   Nevertheless such a difficulty is a problem only of terminology but not of the reality essence, not of its nature, let the reality be either physical (cadaver), or biological (organism), or metaphysical (psyche).