David Hume

“ And thus, tho’ every impression and idea we remember be considered as existent, the idea of existence is not deriv’d from any particular impression.
The idea of existence, then, is the very same with the idea of what we conceive to be existent. To reflect on any thing simply, and to reflect on it as existent, are nothing different from each other. That idea, when conjoin’d with the idea of any object, makes no addition to it. Whatever we conceive, we conceive to be existent. Any idea we please to form is the idea of a being; and the idea of a being is any idea we please to form. ”

“ Let us chase our imagination to the heavens, or to the utmost limits of the universe; we never really advance a step beyond ourselves, nor can conceive any kind of existence, but those perceptions, which have appear’d in that narrow compass. This is the universe of the imagination, nor have we any idea but what is there produc’d.
The farthest we can go towards a conception of external objects, when suppos’d specifically different from our perceptions, is to form a relative idea of them, without pretending to comprehend the related objects. ”

“ In order to know whether any objects, which are join’d in impression, be inseparable in idea, we need only consider, if they be different from each other; in which case, ‘tis plain they may be conceiv’d apart. Every thing, that is different is distinguishable: and everything, that is distinguishable, may be separated, according to the maxims above-explain’d. If on the contrary they be not different, they are not distinguishable: and if they be not distinguishable, they cannot be separated. But this is precisely the case with respect to time, compar’d with our successive perceptions. ”

“ The only defect of our senses is, that they give us disproportion’d images of things, and represent as minute and uncompounded what is really great and compos’d of a vast number of parts. This mistake we are not sensible of: but taking the impressions of those minute objects, which appear to the senses, to be equal or nearly equal to the objects, and finding by reason, that there are other objects vastly more minute, we too hastily conclude, that these are inferior to any idea of our imagination or impression of our senses. ”

“ After this chain of reasoning and explication of my principles, I am now prepar’d to answer all the objections that have been offer’d, whether deriv’d from metaphysics or mechanics. The frequent disputes concerning a vacuum, or extension without matter prove not the reality of the idea, upon which the dispute turns; there being nothing more common, than to see men deceive themselves in this particular; especially when by means of any close relation, there is another idea presented, which may be the occasion of their mistake. ”

“ As ‘tis from the disposition of visible and tangible objects we receive the idea of space, so from the succession of ideas and impressions we form the idea of time, nor is it possible for time alone ever to make its appearance, or be taken notice of by the mind. A man in a sound sleep, or strongly occupy’d with one thought, is insensible of time; and according as his perceptions succeed each other with greater or less rapidity, the same duration appears longer or shorter to his imagination. ”

“ Of the infinite divisibility of our ideas of space and time. Whatever has the air of a paradox, and is contrary to the first and most unprejudiced notions of mankind, is often greedily embrac’d by philosophers, as shewing the superiority of their science, which cou’d discover opinions so remote from vulgar conception. On the other hand, anything propos’d to us, which causes surprize and admiration, gives such a satisfaction to the mind, that it indulges itself in those agreeable emotions, and will never be persuaded that its pleasure is entirely without foundation. ”

“ They never can exist; for we may produce demonstrations from these very ideas to prove, that they are impossible.
But can anything be imagin’d more absurd and contradictory than this reasoning? Whatever can be conceiv’d by a clear and distinct idea necessarily implies the possibility of existence; and he who pretends to prove the impossibility of its existence by any argument derived from the clear idea, in reality asserts, that we have no clear idea of it, because we have a clear idea. ‘Tis in vain to search for a contradiction in any thing that is distinctly conceiv’d by the mind. ”

“ A man who hides himself, confesses as evidently the superiority of his enemy, as another, who fairly delivers his arms.
Thus it appears, that the definitions of mathematics destroy the pretended demonstrations; and that if we have the idea of indivisible points, lines and surfaces conformable to the definition, their existence is certainly possible: but if we have no such idea, ‘tis impossible we can ever conceive the termination of any figure; without which conception there can be no geometrical demonstration. ”

“ Our system concerning space and time consists of two parts, which are intimately connected together. The first depends on this chain of reasoning. The capacity of the mind is not infinite; consequently no idea of extension or duration consists of an infinite number of parts or inferior ideas, but of a finite number, and these simple and indivisible: ‘Tis therefore possible for space and time to exist conformable to this idea: And if it be possible, ‘tis certain they actually do exist conformable to it; since their infinite divisibility is utterly impossible and contradictory. ”

“ But tho’ it be impossible to shew the impression, from which the idea of time without a changeable existence is deriv’d; yet we can easily point out those appearances, which make us fancy we have that idea. For we may observe, that there is a continual succession of perceptions in our mind; so that the idea of time being for ever present with us; when we consider a stedfast object at five-a-clock, and regard the same at six; we are apt to apply to it that idea in the same manner as if every moment were distinguish’d by a different position, or an alteration of the object. ”

“ When I receiv’d the relations of resemblance, contiguity and causation, as principles of union among ideas, without examining into their causes, ‘twas more in prosecution of my first maxim, that we must in the end rest contented with experience, than for want of something specious and plausible, which I might have display’d on that subject. ‘Twou’d have been easy to have made an imaginary dissection of the brain, and have shewn, why upon our conception of any idea, the animal spirits run into all the contiguous traces, and rouze up the other ideas, that are related to it. ”

“ Thus if it be ask’d, whether or not the invisible and intangible distance be always full of body, or of something that by an improvement of our organs might become visible or tangible, I must acknowledge, that I find no very decisive arguments on either side; tho’ I am inclin’d to the contrary opinion, as being more suitable to vulgar and popular notions. If the Newtonian philosophy be rightly understood, it will be found to mean no more. A vacuum is asserted: That is, bodies are said to be plac’d after such a manner, is to receive bodies betwixt them, without impulsion or penetration. ”

“ For as every idea, that is distinguishable, is separable by the imagination; and as every idea, that is separable by the imagination, may be conceiv’d to be separately existent; ‘tis evident, that the existence of one particle of matter, no more implies the existence of another, than a square figure in one body implies a square figure in every one. ”

“ A musician finding his ear becoming every day more delicate, and correcting himself by reflection and attention, proceeds with the same act of the mind, even when the subject fails him, and entertains a notion of a compleat tierce or octave, without being able to tell whence he derives his standard. A painter forms the same fiction with regard to colours. A mechanic with regard to motion. To the one light and shade; to the other swift and slow are imagin’d to be capable of an exact comparison and equality beyond the judgments of the senses. ”

“ These relations betwixt the two kinds of distance will afford us an easy reason, why the one has so often been taken for the other, and why we imagine we have an idea of extension without the idea of any object either of the sight or feeling. For we may establish it as a general maxim in this science of human nature, that wherever there is a close relation betwixt two ideas, the mind is very apt to mistake them, and in all its discourses and reasonings to use the one for the other. ”

“ First, It may be said, that men have disputed for many ages concerning a vacuum and a plenum, without being able to bring the affair to a final decision; and philosophers, even at this day, think themselves at liberty to take part on either side, as their fancy leads them. But whatever foundation there may be for a controversy concerning the things themselves, it may be pretended, that the very dispute is decisive concerning the idea, and that ‘tis impossible men cou’d so long reason about a vacuum, and either refute or defend it, without having a notion of what they refuted or defended. ”

“ The parts, into which the ideas of space and time resolve themselves, become at last indivisible; and these indivisible parts, being nothing in themselves, are inconceivable when not fill’d with something real and existent. The ideas of space and time are therefore no separate or distinct ideas, but merely those of the manner or order, in which objects exist: Or in other words, ‘tis impossible to conceive either a vacuum and extension without matter, or a time, when there was no succession or change in any real existence. ”

“ At the same time we may learn the reason, why geometry falls of evidence in this single point, while all its other reasonings command our fullest assent and approbation. And indeed it seems more requisite to give the reason of this exception, than to shew, that we really must make such an exception, and regard all the mathematical arguments for infinite divisibility as utterly sophistical. For ‘tis evident, that as no idea of quantity is infinitely divisible, there cannot be imagin’d a more glaring absurdity, than to endeavour to prove, that quantity itself admits of such a division ”

“ Now since this distance causes no perception different from what a blind man receives from his eyes, or what is convey’d to us in the darkest night, it must partake of the same properties: And as blindness and darkness afford us no ideas of extension, ‘tis impossible that the dark and undistinguishable distance betwixt two bodies can ever produce that idea. ”

“ To talk therefore of objections and replies, and ballancing of arguments in such a question as this, is to confess, either that human reason is nothing but a play of words, or that the person himself, who talks so, has not a capacity equal to such subjects. ”

“ Having therefore found, that time in its first appearance to the mind is always conjoin’d with a succession of changeable objects, and that otherwise it can never fall under our notice, we must now examine whether it can be conceiv’d without our conceiving any succession of objects, and whether it can alone form a distinct idea in the imagination. ”

“ If the second part of my system be true, that the idea of space or extension is nothing but the idea of visible or tangible points distributed in a certain order; it follows, that we can form no idea of a vacuum, or space, where there is nothing visible or tangible. ”

“ There are many philosophers, who refuse to assign any standard of equality, but assert, that ‘tis sufficient to present two objects, that are equal, in order to give us a just notion of this proportion. ”

“ It has often been maintained in the schools, that extension must be divisible, in infinitum, because the system of mathematical points is absurd; and that system is absurd, because a mathematical point is a non-entity, and consequently can never by its conjunction with others form a real existence. This wou’d be perfectly decisive, were there no medium betwixt the infinite divisibility of matter, and the non-entity of mathematical points. ”

“ But no object can be presented resembling some object with respect to its existence, and different from others in the same particular; since every object, that is presented, must necessarily be existent. ”

“ We may apply the same reasoning to Curve and Right lines. Nothing is more apparent to the senses, than the distinction betwixt a curve and a right line; nor are there any ideas we more easily form than the ideas of these objects. But however easily we may form these ideas, ‘tis impossible to produce any definition of them, which will fix the precise boundaries betwixt them. When we draw lines upon paper, or any continu’d surface, there is a certain order, by which the lines run along from one point to another, that they may produce the entire impression of a curve or right line ”

“ In vain shou’d we have recourse to the common topic, and employ the supposition of a deity, whose omnipotence may enable him to form a perfect geometrical figure, and describe a right line without any curve or inflexion. As the ultimate standard of these figures is deriv’d from nothing but the senses and imagination, ‘tis absurd to talk of any perfection beyond what these faculties can judge of; since the true perfection of any thing consists in its conformity to its standard. ”