Indeed, the finite in its very conception implies an Infinite and the distinction between minds and extended things implies the dependence of these upon an absolute ground or God. Ulti mately, all certainty of knowledge rests on the necessity of accepting the existence of an absolute ground, and the very notion we have of such an absolute ground involves the notion of neces sary existence. In this one case at least it is as legitimate as it is necessary to take thought as a perfectly adequate assurance of objective reality. And, since veracity must be one of the attributes of a perfect being, we have secured additional confirmation of our knowledge of finite facts. For it is through clear and distinct ideas that we apprehend truth, and these ideas the finite mind does not produce but accepts. The question, indeed, forces itself here to the front as to how that obscurity through which we fall into error arises at all, and Descartes attempted to answer it by drawing a radical distinction between understanding and will. The understanding is passive; in strictness the term is but a collective one for the several ideas which the mind possesses. The will, on the other hand, is active, and a more or less arbitrary power; and, in its function of judging, it is not constrained to operate in accordance with truth, and may bring about the result that we take for clear ideas what are in fact the reverse of clear as, for example, when we are led to suppose that the vague, con fused sensations of colour, hardness and so on are objective char acteristics of a material thing. These sensations are not ideas, and it is doubtful whether of them we have so much as images. If, then, by an arbitrary act of will we assume that what is thus in distinct and confused corresponds to reality, we are deceiving ourselves.
induces us to assert the existence of material entities correspond ing to these "ideas" is the complex of confused imagery and corporeal feeling, produced by bodily stimulation. On the oc casion of such stimulation, there occur "modalities," or modifica tions, of the mind—acts of "sensing"—and through these we become aware of the primary and essential qualities, the ideas, of things. The "ideas" are universal, each "modality" or operation of the mind is particular; the "ideas" are immutable, our modes of perceiving are all of them temporal in character.
In the awareness of a concrete thing, there are. then, involved (a) the "idea" or essence, more or less confusedly apprehended, of extendedness, and (b) the complex of sensations or feelings (sentiments), which we erroneously suppose to represent qualities of external things. Thus Malebranche was driven to the conclu sion that we do not know but only infer the concrete existence of material things; and, indeed, although on theological grounds, he was assured of their existence, he made no attempt to explain how "intelligible extension" (the essence of extension in the divine mind), containing as it did no particularising features, can be determined to manifest itself in the form of concrete entities. Obviously, strictly in accordance with the principles of the Cartesian system, the existence and nature of the external world ought to have been shown to be involved in the existence and nature of the infinite ground. To such a position both Descartes himself and Malebranche were always disinclined, although it alone would have made the system even apparently coherent. The step was taken by Spinoza (1632-1677). Spinoza follows Des cartes in regarding what Locke called "secondary qualities," as being simply appearances, having nothing corresponding to them in corporeal nature except figures and motions. But the material universe or res extensa is, in his view, no creation of God; it is an Attribute of God's nature, a form of God's being.
Briefly, Spinoza's monistic philosophy is based upon the funda mental distinction between "substantial" or self-dependent being and "modal" or dependent being, between that which is "in itself" (in se) and conceived "through itself" (per se) and that which is "in another" (in alio) and is conceived through that other.
Whereas for Aristotle finite individual entities were alone entitled to be called "substances," as the subjects of predicates, it is the contention of Spinoza that, when considered in the light of its antecedents, every finite individual entity will be found to have forfeited its supposed substantive character and will turn out to be itself predicable as a phase or modification of something else. Consequently, there can be but one self-dependent Being or Substance, namely, Reality in its entirety and completeness.