1. Uncompounded appearances. The better to understand the nature, manner, and extent of our knowledge, one thing is carefully to be observed concerning the ideas we have ; and that is, that some of them are simple and some complex.
Though the qualities that affect our senses are, in the things themselves, so united and blended, that there is no separation, no distance between them ; yet it is plain, the ideas they produce in the mind enter by the senses simple and unmixed. For, though the sight and touch often take in from the same object, at the same time, different ideas ; – as a man sees at once motion and colour ; the hand feels softness and warmth in the same piece of wax : yet the simple ideas thus united in the same subject, are as perfectly distinct as those that come in by different senses. The coldness and hardness which a man feels in a piece of ice being as distinct ideas in the mind as the smell and whiteness of a lily ; or as the taste of sugar, and smell of a rose. And there is nothing can be plainer to a man than the clear and distinct perception he has of those simple ideas ; which, being each in itself uncompounded, contains in it nothing but one uniform appearance, or conception in the mind, and is not distinguishable into different ideas.
2. The mind can neither make nor destroy them. These simple ideas, the materials of all our knowledge, are suggested and furnished to the mind only by those two ways above mentioned, viz. sensation and reflection. When the understanding is once stored with these simple ideas, it has the power to repeat, compare, and unite them, even to an almost infinite variety, and so can make at pleasure new complex ideas. But it is not in the power of the most exalted wit, or enlarged understanding, by any quickness or variety of thought, to invent or frame one new simple idea in the mind, not taken in by the ways before mentioned : nor can any force of the understanding destroy those that are there. The dominion of man, in this little world of his own understanding being muchwhat the same as it is in the great world of visible things ; wherein his power, however managed by art and skill, reaches no farther than to compound and divide the materials that are made to his hand ; but can do nothing towards the making the least particle of new matter, or destroying one atom of what is already in being. The same inability will every one find in himself, who shall go about to fashion in his understanding one simple idea, not received in by his senses from external objects, or by reflection from the operations of his own mind about them. I would have any one try to fancy any taste which had never affected his palate ; or frame the idea of a scent he had never smelt : and when he can do this, I will also conclude that a blind man hath ideas of colours, and a deaf man true distinct notions of sounds.
3. Only the qualities that affect the senses are imaginable. This is the reason why – though we cannot believe it impossible to God to make a creature with other organs, and more ways to convey into the understanding the notice of corporeal things than those five, as they are usually counted, which he has given to man – yet I think it is not possible for any man to imagine any other qualities in bodies, howsoever constituted, whereby they can be taken notice of, besides sounds, tastes, smells, visible and tangible qualities. And had mankind been made but with four senses, the qualities then which are the objects of the fifth sense had been as far from our notice, imagination, and conception, as now any belonging to a sixth, seventh, or eighth sense can possibly be ; – which, whether yet some other creatures, in some other parts of this vast and stupendous universe, may not have, will be a great presumption to deny. He that will not set himself proudly at the top of all things, but will consider the immensity of this fabric, and the great variety that is to be found in this little and inconsiderable part of it which he has to do with, may be apt to think that, in other mansions of it, there may be other and different intelligent beings, of whose faculties he has as little knowledge or apprehension as a worm shut up in one drawer of a cabinet hath of the senses or understanding of a man ; such variety and excellency being suitable to the wisdom and power of the Maker. I have here followed the common opinion of man’s having but five senses ; though, perhaps, there may be justly counted more ; – but either supposition serves equally to my present purpose.