[73] (1) It only remains for us to inquire by what power our mind can form true ideas, and how far such power extends. (2) It is certain that such power cannot extend itself infinitely. (3) For when we affirm somewhat of a thing, which is not contained in the concept we have formed of that thing, such an affirmation shows a defect of our perception, or that we have formed fragmentary or mutilated ideas. (4) Thus we have seen that the notion of a semicircle is false when it is isolated in the mind, but true when it is associated with the concept of a sphere, or of some cause determining such a motion. (73:5) But if it be the nature of a thinking being, as seems, prima facie, to be the case, to form true or adequate thoughts, it is plain that inadequate ideas arise in us only because we are parts of a thinking being, whose thoughts--some in their entirety, others in fragments only--constitute our mind. [74] (1) But there is another point to be considered, which was not worth raising in the case of fiction, but which give rise to complete deception--namely, that certain things presented to the imagination also exist in the understanding--in other words, are conceived clearly and distinctly. (2) Hence, so long as we do not separate that which is distinct from that which is confused, certainty, or the true idea, becomes mixed with indistinct ideas. (3) For instance, certain Stoics heard, perhaps, the term "soul," and also that the soul is immortal, yet imagined it only confusedly; they imaged, also, and understood that very subtle bodies penetrate all others, and are penetrated by none. (74:4) By combining these ideas, and being at the same time certain of the truth of the axiom, they forthwith became convinced that the mind consists of very subtle bodies; that these very subtle bodies cannot be divided &c. [75] (1) But we are freed from mistakes of this kind, so long as we endeavor to examine all our perceptions by the standard of the given true idea. (2) We must take care, as has been said, to separate such perceptions from all those which arise from hearsay or unclassified experience. (3) Moreover, such mistakes arise from things being conceived too much in the abstract; for it is sufficiently self-evident that what I conceive as in its true object I cannot apply to anything else. (75:4) Lastly, they arise from a want of understanding of the primary elements of nature as a whole; whence we proceed without due order, and confound nature with abstract rules, which, although they be true enough in their sphere, yet, when misapplied, confound themselves, and pervert the order of nature. (5) However, if we proceed with as little abstraction as possible, and begin from primary elements--that is, from the source and origin of nature, as far back as we can reach,--we need not fear any deceptions of this kind.