I recognize by observation that bodies are heavy. I can cognize
beforehand by analysis the conception of body through the
characteristics of extension, impenetrability, shape, etc., all
which are cogitated in this conception. But now I extend my knowledge,
and looking back on experience from which I had derived this
conception of body, I find weight at all times connected with the
above characteristics, and therefore I synthetically add to my
conceptions this as a predicate, and say, "All bodies are heavy." Thus
it is experience upon which rests the possibility of the synthesis
of the predicate of weight with the conception of body, because both
conceptions, although the one is not contained in the other, still
belong to one another (only contingently, however), as parts of a
whole, namely, of experience, which is itself a synthesis of
intuitions.

But to synthetical judgements a priori, such aid is entirely
wanting. If I go out of and beyond the conception A, in order to
recognize another B as connected with it, what foundation have I to
rest on, whereby to render the synthesis possible? I have here no
longer the advantage of looking out in the sphere of experience for
what I want. Let us take, for example, the proposition, "Everything
that happens has a cause." In the conception of "something that
happens," I indeed think an existence which a certain time
antecedes, and from this I can derive analytical judgements. But the
conception of a cause lies quite out of the above conception, and
indicates something entirely different from "that which happens,"
and is consequently not contained in that conception. How then am I
able to assert concerning the general conception--"that which
happens"--something entirely different from that conception, and to
recognize the conception of cause although not contained in it, yet