BOOK I PART I
and causation. The effect of this is, that what-
ever new simple quality we discover to have
the same connexion with the rest, we immedi-
ately comprehend it among them, even though
it did not enter into the first conception of the
substance. Thus our idea of gold may at first be
a yellow colour, weight, malleableness, fusibil-
ity; but upon the discovery of its dissolubility
in aqua regia, we join that to the other quali-
ties, and suppose it to belong to the substance
as much as if its idea had from the beginning
made a part of the compound one. The princi-
pal of union being regarded as the chief part of
the complex idea, gives entrance to whatever
quality afterwards occurs, and is equally com-
prehended by it, as are the others, which first
presented themselves.
That this cannot take place in modes, is evi-