Next to the nature and operation of the cosmos the greatest puzzle in philosophy and science is the nature and operation of the mind. If it is difficult to reconcile an omnipotent benevolence with the neutrality of nature and the fatality of suffering, it seems just as hard to understand how an apparently external and material object in space can generate an apparently immaterial and spaceless idea, or how an idea in the mind can become a motion in the body, or how idea can contemplate idea in the mystery of consciousness.
Spinoza tries to avoid some of these problems by rejecting Descartes’ assumption that body and mind are two different substances. Body and mind, he believes, are one and the same reality, perceived under two different aspects or attributes, just as extension and thought are one in God. There is then no problem of how body acts upon mind or vice versa; every action is the simultaneous and unified operation of both body and mind. Spinoza defines mind as “the idea of the body”; 97 i.e., it is the psycho-
logical (not necessarily the conscious) correlate or accompaniment of a physiological process. The mind is the body felt from within; the body is the mind seen from without. A mental state is the inside, or internal aspect, of bodily action. An act of “will” is the mental accompaniment of a bodily desire that is moving into physical expression. There is no action of the “will” upon the body; there is a single action of the psychophysical (mentalmaterial) organism; the “will” is not the cause, it is the consciousness of the action. “The decision of the mind, and the desire and determination of the body are . . . one and the same thing, which, when considered under the attribute of thought . . . , we call a decision (decretum), and which, when considered under the attribute of extension, and deduced from the laws of motion and rest, is called a determination” (a finished action). 98 Hence “the order of the actions and passions [movements] of our body are simultaneous in nature with the order and passions of the mind.” 99 In all cases of the supposed interaction of mind and body the actual process is not the interplay of two distinct realities, substances, or agents, but the single action of one substance, which, seen from outside, we call body, and which, seen from within, we call mind. To every process in the body there is a corresponding process in the mind; “nothing can happen in the body which is not perceived by the mind.” 100 But this mental correlate need not be a thought; it may be a feeling; and it need not be conscious; so a sleepwalker performs any number of actions while he is “unconscious.” 101 This theory has been called “psychophysical parallelism”; however, it supposes parallel processes not in two different entities, but in one psychophysical unity doubly seen.
On this basis Spinoza proceeds to a mechanistic description of the knowledge process. Probably following Hobbes, he defines sensation, memory, and imagination in physical terms. 102 He takes it as evident that most knowledge originates in impressions made upon us by external objects; but he admits to the idealist that “the human mind perceives no external body as actually existing save through ideas of modifications in its body.” 103 Perception and reason, two forms of knowledge, are derived from sensation; but a third and higher form, “intuitive knowledge,” is derived (Spinoza thinks) not from sensation but from a clear, distinct, immediate, and comprehensive awareness of an idea or event as part of a universal system of law.
Anticipating Locke and Hume, Spinoza rejects the notion that the mind is an agent or entity possessing ideas; “mind” is a general or abstract term for the succession of perceptions, memories, imaginations, feelings, and other mental states. “The idea of the mind, and the mind itself” at any moment, “are one and the same thing.” 104 Nor are there any distinct “faculties” such as intellect or will; these also are abstract terms for the sum of cognitions or volitions; “intellect or will have reference in the same manner to this or that idea, or to this or that volition, as ‘stoniness’ to this or that stone, or ‘man’ to Peter or Paul.” 105 Neither do idea and volition differ; a volition or act of “will” is merely an idea that has “affirmed itself” 106 (i.e., has lasted long enough to complete itself in an action, as ideas, if unimpeded, automatically do). “The decision of the mind . . . is nothing but the affirmation which the idea necessarily involves insofar as it is an idea 107 . . . Will and intellect are one and the same thing.” 108
From another standpoint what we call will is simply the sum and play of desires. “By desire . . . I understand all the efforts, impulses, appetites, and volitions of a man, which . . . not infrequently are so opposed to one another that he is drawn hither and thither, and knows not where to turn.” 109 Deliberation is the alternating domination of body-and-thought by conflicting desires; it ends when one desire proves powerful enough to maintain its corresponding mental state long enough to pass into action. Obviously (says Spinoza) there is no “free will”; the will at any moment is just the strongest desire. We are free insofar as we are allowed to express our nature or our desires without external hindrance; we are not free to choose our own nature or our desires; we are our desires. “There is in no mind absolute or free will, but the mind is determined for willing this or that by a cause which is determined in its turn by another cause, and this again by another, and so on to infinity.” 110 “Men think themselves free because they are conscious of their volitions and desires, but are ignorant of the causes by which they are led to wish and desire”; 111 it is as if a stone flung through space should think it is moving and falling of its own will. 112
Possibly the Calvinist fatalism in the “climate of opinion” that Descartes and Spinoza lived in as residents of Holland may have shared with the Galilean mechanics (Newton’s Principia had not yet appeared) in molding the mechanistic theory in Descartes and the determinist psychology in Spinoza. Determinism is predestinarianism without theology; it substitutes the primeval vortex or nebula for God. Spinoza followed the logic of mechanism to its bitter end; he did not, like Descartes, confine it to bodies and animals; he applied it to minds as well, as he had to, since to him mind and body were one. He concluded that the body is a machine, 113 but he denied that determinism makes morality useless or insincere. The exhortations of the moralist, the ideals of the philosophers, the stigma of public condemnation, and the penalties of the courts are still valuable and necessary; they enter into the heritage and experience of the growing individual, and therefore into the factors that form his desires and determine his will.