SIR, As all the ideas or images of the brain must be caused originally by impressions of objects without us, so we can reason upon no other. A man born blind can have no image of light or colours; nor one who has been always deaf, of sounds; whatever descriptions are given him of them. There are many creatures in the world who want some organs of sense which we have, and probably there are others in the universe which have many that we want: and such beings, if there be any such, must know many things of which we have no conception; and must judge of other things, of which we have a more partial conception, in different lights from what we are capable of judging. It is not certain that any two men see colours in the same lights; and it is most certain, that the same men at different times, according to the good or evil disposition of their organs, see them in various ones, and consequently their ratiocinations upon them will be different; which experience shews us to be true in distempered, enthusiastick, or melancholy men.
Our senses are evidently adapted to take in only finite or limited beings; nor are we capable of conceiving their existence, otherwise than by mediums of extension and solidity. The mind finds that it sees, hears, tastes, smells, and feels, which is its manner of first conceiving things, or in other words, is the modus in which objects affect it; and it can reason no farther upon them, than according to those impressions: So that it is conversant only about the film or outside of bodies, and knows nothing of their internal contexture, or how they perform their operations; and consequently can affirm or deny nothing about them; but according to the perceptions which it has. When it goes further, or attempts to go further, it rambles in the dark, wades out of its depth, and must rave about non-entities, or, which is the same thing to us, about what we do or can know nothing of, or nothing to the purpose; and yet these things, or these nothings, have employed the leisure, speculations, and pens of many very learned men, as if true wisdom consisted in knowing what we want faculties to know.
All that we can know of infinity, eternity, &c. is, that we can know little or nothing about them. We must understand what we mean by the terms, or else we could not use them, or must use them impertinently. We perfectly apprehend what we mean by duration, which is our conception of the continuance of things, and contains in it a terminus a quo to a terminus ad quem, that is, it has certain boundaries in our imaginations, and we can multiply this conception backwards and forwards, without ever being able to come to the end of it, and so may be sure that it is without end; and then the imagination is lost, and can go no further. We know that all extended bodies are divisible and can never be divided so often, but they may be divided farther; and therefore say justly, they are infinitely divisible; nor can any body be so large or long, as to come to the end of extension. And therefore we may safely affirm, that extension or space (which is our conception of the existence and immensity of bodies) is infinite. But then we know no other properties of infinity or eternity, but by the help of these conceptions, which being limited and finite, cannot measure what is infinite and eternal; that is, we cannot comprehend what is incomprehensible to any being which is not infinite and eternal too, and whose existence is not as unmeasurable by time and place as those images are.
All the disputes, seeming contradictions, and absurdities, which offer themselves when we think or talk of infinity or eternity, arise from our applying our thoughts, which are confined to finite beings, and our words, which are coined to convey finite conceptions, to subjects which are infinite, and of which we can have no adequate ideas that can be expressed by sounds. Nothing is more true in finite beings, than that the whole must consist of all its parts; but in infinity there is no whole, nor consequently parts. Where there is no beginning, nor any end, there can be no middle; and where there is no whole, there can be no half. Time or space in theory are not divisible, because nothing but time or space can divide them, and then they are not divided; yet we know that time or space, as they have relation to finite beings, and our existence of duration, may be divided, and are so; and therefore the riddles made about them are owing to the narrowness of our capacities, and to our endeavouring to apply such conceptions as we have, to objects of which we can have no conception; which is, in effect, to attempt to hear sights, and see sounds.