48.  The Abstract Ideas of Substances always imperfect and therefore various.

But this is not all.  It would also follow that the names of substances would not only have, as in truth they have, but would also be supposed to have different significations, as used by different men, which would very much cumber the use of language.  For if every distinct quality that were discovered in any matter by any one were supposed to make a necessary part of the complex idea signified by the common name given to it, it must follow, that men must suppose the same word to signify different things in different men:  since they cannot doubt but different men may have discovered several qualities, in substances of the same denomination, which others know nothing of.

49.  Therefore to fix the Nominal Species Real Essence supposed.

To avoid this therefore, they have supposed a real essence belonging to every species, from which these proper ties all flow, and would have their name of the species stand for that.  But they, not having any idea of that real essence in substances, and their words signifying nothing but the ideas they have, that which is done by this attempt is only to put the name or sound in the place and stead of the thing having that real essence, without knowing what the real essence is, and this is that which men do when they speak of species of things, as supposing them made by nature, and distinguished by real essences.

50.  Which Supposition is of no Use.

For, let us consider, when we affirm that ‘all gold is fixed,’ either it means that fixedness is a part of the definition, i. e., part of the nominal essence the word gold stands for; and so this affirmation, ’all gold is fixed,’ contains nothing but the signification of the term gold.  Or else it means, that fixedness, not being a part of the definition of the gold, is a property of that substance itself:  in which case it is plain that the word gold stands in the place of a substance, having the real essence of a species of things made by nature.  In which way of substitution it has so confused and uncertain a signification, that, though this proposition—­’gold is fixed’—­be in that sense an affirmation of something real; yet it is a truth will always fail us in its particular application, and so is of no real use or certainty.  For let it be ever so true, that all gold, i. e. all that has the real essence of gold, is fixed, what serves this for, whilst we know not, in this sense, what is or is not gold?  For if we know not the real essence of gold, it is impossible we should know what parcel of matter has that essence, and so whether it be true gold or no.

51.  Conclusion.