1. Treating of words necessary to knowledge. Though the examining and judging of ideas by
themselves, their names being quite laid aside, be the best and surest way to clear and distinct
knowledge: yet, through the prevailing custom of using sounds for ideas, I think it is very seldom
practised. Every one may observe how common it is for names to be made use of, instead of the
ideas themselves, even when men think and reason within their own breasts; especially if the ideas
be very complex, and made up of a great collection of simple ones. This makes the consideration of
words and propositions so necessary a part of the Treatise of Knowledge, that it is very hard to
speak intelligibly of the one, without explaining the other.
2. General truths hardly to be understood, but in verbal propositions. All the knowledge we have,
being only of particular or general truths, it is evident that whatever may be done in the former of
these, the latter, which is that which with reason is most sought after, can never be well made
known, and is very seldom apprehended, but as conceived and expressed in words. It is not,
therefore, out of our way, in the examination of our knowledge, to inquire into the truth and certainty
of universal propositions.
3. Certainty twofold--of truth and of knowledge. But that we may not be misled in this case by that
which is the danger everywhere, I mean by the doubtfulness of terms, it is fit to observe that
certainty is twofold: certainty of truth and certainty of knowledge. Certainty of truth is, when words
are so put together in propositions as exactly to express the agreement or disagreement of the
ideas they stand for, as really it is. Certainty of knowledge is to perceive the agreement or
disagreement of ideas, as expressed in any proposition. This we usually call knowing, or being
certain of the truth of any proposition.
4. No proposition can be certainly known to be true, where the real essence of each species
mentioned is not known. Now, because we cannot be certain of the truth of any general proposition,
unless we know the precise bounds and extent of the species its terms stand for, it is necessary we
should know the essence of each species, which is that which constitutes and bounds it.
This, in all simple ideas and modes, is not hard to do. For in these the real and nominal essence
being the same, or, which is all one, the abstract idea which the general term stands for being the
sole essence and boundary that is or can be supposed of the species, there can be no doubt how
far the species extends, or what things are comprehended under each term; which, it is evident, are
all that have an exact conformity with the idea it stands for, and no other.
But in substances, wherein a real essence, distinct from the nominal, is supposed to constitute,
determine, and bound the species, the extent of the general word is very uncertain; because, not
knowing this real essence, we cannot know what is, or what is not of that species; and,
consequently, what may or may not with certainty be affirmed of it. And thus, speaking of a man, or
gold, or any other species of natural substances, as supposed constituted by a precise and real
essence which nature regularly imparts to every individual of that kind, whereby it is made to be of
that species, we cannot be certain of the truth of any affirmation or negation made of it. For man or
gold, taken in this sense, and used for species of things constituted by real essences, different from
the complex idea in the mind of the speaker, stand for we know not what; and the extent of these
species, with such boundaries, are so unknown and undetermined, that it is impossible with any
certainty to affirm, that all men are rational, or that all gold is yellow. But where the nominal essence
is kept to, as the boundary of each species, and men extend the application of any general term no
further than to the particular things in which the complex idea it stands for is to be found, there they
are in no danger to mistake the bounds of each species, nor can be in doubt, on this account,
whether any proposition be true or not. I have chosen to explain this uncertainty of propositions in
this scholastic way, and have made use of the terms of essences, and species, on purpose to show
the absurdity and inconvenience there is to think of them as of any other sort of realities, than barely
abstract ideas with names to them. To suppose that the species of things are anything but the
sorting of them under general names, according as they agree to several abstract ideas of which we
make those names the signs, is to confound truth, and introduce uncertainty into all general
propositions that can be made about them. Though therefore these things might, to people not
possessed with scholastic learning, be treated of in a better and clearer way; yet those wrong
notions of essences or species having got root in most people's minds who have received any
tincture from the learning which has prevailed in this part of the world, are to be discovered and
removed, to make way for that use of words which should convey certainty with it.
5. This more particularly concerns substances. The names of substances, then, whenever made to
stand for species which are supposed to be constituted by real essences which we know not, are
not capable to convey certainty to the understanding. Of the truth of general propositions made up
of such terms we cannot be sure. The reason whereof is plain: for how can we be sure that this or
that quality is in gold, when we know not what is or is not gold? Since in this way of speaking,
nothing is gold but what partakes of an essence, which we, not knowing, cannot know where it is or
is not, and so cannot be sure that any parcel of matter in the world is or is not in this sense gold;
being incurably ignorant whether it has or has not that which makes anything to be called gold; i.e.,
that real essence of gold whereof we have no idea at all. This being as impossible for us to know as
it is for a blind man to tell in what flower the colour of a pansy is or is not to be found, whilst he has
no idea of the colour of a pansy at an. Or if we could (which is impossible) certainly know where a
real essence, which we know not, is, v.g. in what parcels of matter the real essence of gold is, yet
could we not be sure that this or that quality could with truth be affirmed of gold; since it is
impossible for us to know that this or that quality or idea has a necessary connexion with a real
essence of which we have no idea at all, whatever species that supposed real essence may be
imagined to constitute.
6. The truth of few universal propositions concerning substances is to be known. On the other side,
the names of substances, when made use of as they should be, for the ideas men have in their
minds, though they carry a clear and determinate signification with them, will not yet serve us to
make many universal propositions of whose truth we can be certain. Not because in this use of
them we are uncertain what things are signified by them, but because the complex ideas they stand
for are such combinations of simple ones as carry not with them any discoverable connexion or
repugnancy, but with a very few other ideas.
7. Because necessary co-existence of simple ideas in substances can in few cases be known. The
complex ideas that our names of the species of substances properly stand for, are collections of
such qualities as have been observed to co-exist in an unknown substratum, which we call
substance; but what other qualities necessarily co-exist with such combinations, we cannot certainly
know, unless we can discover their natural dependence; which, in their primary qualities, we can go
but a very little way in; and in all their secondary qualities we can discover no connexion at all: for
the reasons mentioned, chap. iii. Viz., 1. Because we know not the real constitutions of substances,
on which each secondary quality particularly depends. 2. Did we know that, it would serve us only
for experimental (not universal) knowledge; and reach with certainty no further than that bare
instance: because our understandings can discover no conceivable connexion between any
secondary quality and any modification whatsoever of any of the primary ones. And therefore there
are very few general propositions to be made concerning substances, which can carry with them
undoubted certainty.
8. Instance in gold. "All gold is fixed," is a proposition whose truth we cannot be certain of, how
universally soever it be believed. For if, according to the useless imagination of the Schools, any
one supposes the term gold to stand for a species of things set out by nature, by a real essence
belonging to it, it is evident he knows not what particular substances are of that species; and so
cannot with certainty affirm anything universally of gold. But if he makes gold stand for a species
determined by its nominal essence, let the nominal essence, for example, be the complex idea of a
body of a certain yellow colour, malleable, fusible, and heavier than any other known;--in this proper
use of the word gold, there is no difficulty to know what is or is not gold. But yet no other quality can
with certainty be universally affirmed or denied of gold, but what hath a discoverable connexion or
inconsistency with that nominal essence. Fixedness, for example, having no necessary connexion
that we can discover, with the colour, weight, or any other simple idea of our complex one, or with
the whole combination together; it is impossible that we should certainly know the truth of this
proposition, that all gold is fixed.
9. No discoverable necessary connexion between nominal essence of gold and other simple ideas.
As there is no discoverable connexion between fixedness and the colour, weight, and other simple
ideas of that nominal essence of gold; so, if we make our complex idea of gold, a body yellow,
fusible, ductile, weighty, and fixed, we shall be at the same uncertainty concerning solubility in aqua
regia, and for the same reason. Since we can never, from consideration of the ideas themselves,
with certainty affirm or deny of a body whose complex idea is made up of yellow, very weighty,
ductile, fusible, and fixed, that it is soluble in aqua regia: and so on of the rest of its qualities. I would
gladly meet with one general affirmation concerning any quality of gold, that any one can certainly
know is true. It will, no doubt, be presently objected, Is not this an universal proposition, Al gold is
malleable? To which I answer, It is a very certain proposition, if malleableness be a part of the
complex idea the word gold stands for. But then here is nothing affirmed of gold, but that that sound
stands for an idea in which malleableness is contained: and such a sort of truth and certainty as this
it is, to say a centaur is four-footed. But if malleableness make not a part of the specific essence the
name of gold stands for, it is plain, all gold is malleable, is not a certain proposition. Because, let the
complex idea of gold be made up of whichsoever of its other qualities you please, malleableness
will not appear to depend on that complex idea, nor follow from any simple one contained in it: the
connexion that malleableness has (if it has any) with those other qualities being only by the
intervention of the real constitution of its insensible parts; which, since we know not, it is impossible
we should perceive that connexion, unless we could discover that which ties them together.
10. As far as any such co-existence can be known, so far universal propositions may be certain. But
this will go but a little way. The more, indeed, of these coexisting qualities we unite into one complex
idea, under one name, the more precise and determinate we make the signification of that word; but
never yet make it thereby more capable of universal certainty, in respect of other qualities not
contained in our complex idea: since we perceive not their connexion or dependence on one
another; being ignorant both of that real constitution in which they are all founded, and also how
they flow from it. For the chief part of our knowledge concerning substances is not, as in other
things, barely of the relation of two ideas that may exist separately; but is of the necessary
connexion and co-existence of several distinct ideas in the same subject, or of their repugnancy so
to co-exist. Could we begin at the other end, and discover what it was wherein that colour consisted,
what made a body lighter or heavier, what texture of parts made it malleable, fusible, and fixed, and
fit to be dissolved in this sort of liquor, and not in another;--if, I say, we had such an idea as this of
bodies, and could perceive wherein all sensible qualities originally consist, and how they are
produced; we might frame such abstract ideas of them as would furnish us with matter of more
general knowledge, and enable us to make universal propositions, that should carry general truth
and certainty with them. But whilst our complex ideas of the sorts of substances are so remote from
that internal real constitution on which their sensible qualities depend, and are made up of nothing
but an imperfect collection of those apparent qualities our senses can discover, there can be few
general propositions concerning substances of whose real truth we can be certainly assured; since
there are but few simple ideas of whose connexion and necessary coexistence we can have certain
and undoubted knowledge. I imagine, amongst all the secondary qualities of substances, and the
powers relating to them, there cannot any two be named, whose necessary co-existence, or
repugnance to coexist, can certainly be known; unless in those of the same sense, which
necessarily exclude one another, as I have elsewhere shown. No one, I think, by the colour that is in
any body, can certainly know what smell, taste, sound, or tangible qualities it has, nor what
alterations it is capable to make or receive on or from other bodies. The same may be said of the
sound or taste, etc. Our specific names of substances standing for any collections of such ideas, it
is not to be wondered that we can with them make very few general propositions of undoubted real
certainty. But yet so far as any complex idea of any sort of substances contains in it any simple idea,
whose necessary existence with any other may be discovered, so far universal propositions may
with certainty be made concerning it: v.g. could any one discover a necessary connexion between
malleableness and the colour or weight of gold, or any other part of the complex idea signified by
that name, he might make a certain universal proposition concerning gold in this respect; and the
real truth of this proposition, that all gold is malleable, would be as certain as of this, the three
angles of all right-lined triangles are all equal to two right ones.
11. The qualities which make our complex ideas of substances depend mostly on external, remote,
and unperceived causes. Had we such ideas of substances as to know what real constitutions
produce those sensible qualities we find in them, and how those qualities flowed from thence, we
could, by the specific ideas of their real essences in our own minds, more certainly find out their
properties, and discover what qualities they had or had not, than we can now by our senses: and to
know the properties of gold, it would be no more necessary that gold should exist, and that we
should make experiments upon it, than it is necessary for the knowing the properties of a triangle,
that a triangle should exist in any matter, the idea in our minds would serve for the one as well as
the other. But we are so far from being admitted into the secrets of nature, that we scarce so much
as ever approach the first entrance towards them. For we are wont to consider the substances we
meet with, each of them, as an entire thing by itself, having all its qualities in itself, and independent
of other things; overlooking, for the most part, the operations of those invisible fluids they are
encompassed with, and upon whose motions and operations depend the greatest part of those
qualities which are taken notice of in them, and are made by us the inherent marks of distinction
whereby we know and denominate them. Put a piece of gold anywhere by itself, separate from the
reach and influence of all other bodies, it will immediately lose all its colour and weight, and perhaps
malleableness too; which, for aught I know, would be changed into a perfect friability. Water, in
which to us fluidity is an essential quality, left to itself, would cease to be fluid. But if inanimate
bodies owe so much of their present state to other bodies without them, that they would not be what
they appear to us were those bodies that environ them removed; it is yet more so in vegetables,
which are nourished, grow, and produce leaves, flowers, and seeds, in a constant succession. And
if we look a little nearer into the state of animals, we shall find that their dependence, as to life,
motion, and the most considerable qualities to be observed in them, is so wholly on extrinsical
causes and qualities of other bodies that make no part of them, that they cannot subsist a moment
without them: though yet those bodies on which they depend are little taken notice of, and make no
part of the complex ideas we frame of those animals. Take the air but for a minute from the greatest
part of living creatures, and they presently lose sense, life, and motion. This the necessity of
breathing has forced into our knowledge. But how many other extrinsical and possibly very remote
bodies do the springs of these admirable machines depend on, which are not vulgarly observed, or
so much as thought on; and how many are there which the severest inquiry can never discover?
The inhabitants of this spot of the universe, though removed so many millions of miles from the sun,
yet depend so much on the duly tempered motion of particles coming from or agitated by it, that
were this earth removed but a small part of the distance out of its present situation, and placed a
little further or nearer that source of heat, it is more than probable that the greatest part of the
animals in it would immediately perish: since we find them so often destroyed by an excess or
defect of the sun's warmth, which an accidental position in some parts of this our little globe
exposes them to. The qualities observed in a loadstone must needs have their source far beyond
the confines of that body; and the ravage made often on several sorts of animals by invisible
causes, the certain death (as we are told) of some of them, by barely passing the line, or, as it is
certain of other, by being removed into a neighbouring country; evidently show that the concurrence
and operations of several bodies, with which they are seldom thought to have anything to do, is
absolutely necessary to make them be what they appear to us, and to preserve those qualities by
which we know and distinguish them. We are then quite out of the way, when we think that things
contain within themselves the qualities that appear to us in them; and we in vain search for that
constitution within the body of a fly or an elephant, upon which depend those qualities and powers
we observe in them. For which, perhaps, to understand them aright, we ought to look not only
beyond this our earth and atmosphere, but even beyond the sun or remotest star our eyes have yet
discovered. For how much the being and operation of particular substances in this our globe
depends on causes utterly beyond our view, is impossible for us to determine. We see and perceive
some of the motions and grosser operations of things here about us; but whence the streams come
that keep all these curious machines in motion and repair, how conveyed and modified, is beyond
our notice and apprehension: and the great parts and wheels, as I may say so, of this stupendous
structure of the universe, may, for aught we know, have such a connexion and dependence in their
influences and operations one upon another, that perhaps things in this our mansion would put on
quite another face, and cease to be what they are, if some one of the stars or great bodies
incomprehensibly remote from us, should cease to be or move as it does. This is certain: things,
however absolute and entire they seem in themselves, are but retainers to other parts of nature, for
that which they are most taken notice of by us. Their observable qualities, actions, and powers are
owing to something without them; and there is not so complete and perfect a part that we know of
nature, which does not owe the being it has, and the excellences of it, to its neighbours; and we
must not confine our thoughts within the surface of any body, but look a great deal further, to
comprehend perfectly those qualities that are in it.
12. Our nominal essences of substances furnish few universal propositions about them that are
certain. If this be so, it is not to be wondered that we have very imperfect ideas of substances, and
that the real essences, on which depend their properties and operations, are unknown to us. We
cannot discover so much as that size, figure, and texture of their minute and active parts, which is
really in them; much less the different motions and impulses made in and upon them by bodies from
without, upon which depends, and by which is formed the greatest and most remarkable part of
those qualities we observe in them, and of which our complex ideas of them are made up. This
consideration alone is enough to put an end to all our hopes of ever having the ideas of their real
essences; which whilst we want, the nominal essences we make use of instead of them will be able
to furnish us but very sparingly with any general knowledge, or universal propositions capable of
real certainty.
13. Judgment of probability concerning substances may reach further: but that is not knowledge. We
are not therefore to wonder, if certainty be to be found in very few general propositions made
concerning substances: our knowledge of their qualities and properties goes very seldom further
than our senses reach and inform us. Possibly inquisitive and observing men may, by strength of
judgment, penetrate further, and, on probabilities taken from wary observation, and hints well laid
together, often guess right at what experience has not yet discovered to them. But this is but
guessing still; it amounts only to opinion, and has not that certainty which is requisite to knowledge.
For all general knowledge lies only in our own thoughts, and consists barely in the contemplation of
our own abstract ideas. Wherever we perceive any agreement or disagreement amongst them,
there we have general knowledge; and by putting the names of those ideas together accordingly in
propositions, can with certainty pronounce general truths. But because the abstract ideas of
substances, for which their specific names stand, whenever they have any distinct and determinate
signification, have a discoverable connexion or inconsistency with but a very few other ideas, the
certainty of universal propositions concerning substances is very narrow and scanty, in that part
which is our principal inquiry concerning them; and there are scarce any of the names of
substances, let the idea it is applied to be what it will, of which we can generally, and with certainty,
pronounce, that it has or has not this or that other quality belonging to it, and constantly co-existing
or inconsistent with that idea, wherever it is to be found.
14. What is requisite for our knowledge of substances. Before we can have any tolerable knowledge
of this kind, we must First know what changes the primary qualities of one body do regularly
produce in the primary qualities of another, and how. Secondly, We must know what primary
qualities of any body produce certain sensations or ideas in us. This is in truth no less than to know
all the effects of matter, under its divers modifications of bulk, figure, cohesion of parts, motion and
rest. Which, I think every body will allow, is utterly impossible to be known by us without revelation.
Nor if it were revealed to us what sort of figure, bulk, and motion of corpuscles would produce in us
the sensation of a yellow colour, and what sort of figure, bulk, and texture of parts in the superficies
of any body were fit to give such corpuscles their due motion to produce that colour; would that be
enough to make universal propositions with certainty, concerning the several sorts of them; unless
we had faculties acute enough to perceive the precise bulk, figure, texture, and motion of bodies, in
those minute parts, by which they operate on our senses, so that we might by those frame our
abstract ideas of them. I have mentioned here only corporeal substances, whose operations seem
to lie more level to our understandings. For as to the operations of spirits, both their thinking and
moving of bodies, we at first sight find ourselves at a loss; though perhaps, when we have applied
our thoughts a little nearer to the con