[71] (1) Wherefore the reality (forma) of true thought must exist in the thought itself, without reference to other thoughts; it does not acknowledge the object as its cause, but must depend on the actual power and nature of the understanding. (2) For, if we suppose that the understanding has perceived some new entity which has never existed, as some conceive the understanding of God before He created thing (a perception which certainly could not arise any object), and has legitimately deduced other thoughts from said perception, all such thoughts would be true, without being determined by any external object; they would depend solely on the power and nature of the understanding. (71:3) Thus, that which constitutes the reality of a true thought must be sought in the thought itself, and deduced from the nature of the understanding.
[72] (1) In order to pursue our investigation, let us confront ourselves with some true idea, whose object we know for certain to be dependent on our power of thinking, and to have nothing corresponding to it in nature. (2) With an idea of this kind before us, we shall, as appears from what has just been said, be more easily able to carry on the research we have in view. (72:3) For instance, in order to form the conception of a sphere, I invent a cause at my pleasure--namely, a semicircle revolving round its center, and thus producing a sphere. (4) This is indisputably a true idea; and, although we know that no sphere in nature has ever actually been so formed, the perception remains true, and is the easiest manner of conceiving a sphere. (72:5) We must observe that this perception asserts the rotation of a semicircle--which assertion would be false, if it were not associated with the conception of a sphere, or of a cause determining a motion of the kind, or absolutely, if the assertion were isolated. (6) The mind would then only tend to the affirmation of the sole motion of a semicircle, which is not contained in the conception of a semicircle, and does not arise from the conception of any cause capable of producing such motion.
(72:7) Thus falsity consists only in this, that something is affirmed of a thing, which is not contained in the conception we have formed of that thing, as motion or rest of a semicircle. (8) Whence it follows that simple ideas cannot be other than true--e.g., the simple idea of a semicircle, of motion, of rest, of quantity, &c.
(72:9) Whatsoever affirmation such ideas contain is equal to the concept formed, and does not extend further. (10) Wherefore we form as many simple ideas as we please, without any fear of error.
[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.
[76] (1) As far as the knowledge of the origin of nature is concerned, there is no danger of our confounding it with abstractions. (2) For when a thing is conceived in the abstract, as are all universal notions, the said universal notions are always more extensive in the mind than the number of individuals forming their contents really existing in nature. (3) Again, there are many things in nature, the difference between which is so slight as to be hardly perceptible to the understanding; so that it may readily happen that such things are confounded together, if they be conceived abstractedly. (4) But since the first principle of nature cannot (as we shall see hereafter) be conceived abstractedly or universally, and cannot extend further in the understanding than it does in reality, and has no likeness to mutable things, no confusion need be feared in respect to the idea of it, provided (as before shown) that we possess a standard of truth. (5) This is, in fact, a being single and infinite [76z]; in other words, it is the sum total of being, beyond which there is no being found. [76a]
[77] (1) Thus far we have treated of the false idea. We have now to investigate the doubtful idea--that is, to inquire what can cause us to doubt, and how doubt may be removed. (2) I speak of real doubt existing in the mind, not of such doubt as we see exemplified when a man says that he doubts, though his mind does not really hesitate. (77:3) The cure of the latter does not fall within the province of method, it belongs rather to inquiries concerning obstinacy and its cure.
[78] (1) Real doubt is never produced in the mind by the thing doubted of. (2) In other words, if there were only one idea in the mind, whether that idea were true or false, there would be no doubt or certainty present, only a certain sensation. (3) For an idea is in itself nothing else than a certain sensation. (4) But doubt will arise through another idea, not clear and distinct enough for us to be able to draw any certain conclusions with regard to the matter under consideration; that is, the idea which causes us to doubt is not clear and distinct. (5) To take an example. (78:6) Supposing that a man has never reflected, taught by experience or by any other means, that our senses sometimes deceive us, he will never doubt whether the sun be greater or less than it appears. (7) Thus rustics are generally astonished when they hear that the sun is much larger than the earth. (8) But from reflection on the deceitfulness of the senses [78a] doubt arises, and if, after doubting, we acquire a true knowledge of the senses, and how things at a distance are represented through their instrumentality, doubt is again removed.