oints is a straight line." We cannot even conceive of the
contrary. Therefore these axioms have no reasons, and can neither be
deduced nor proved. Every question as to their reasons is quite
meaningless. As examples of a "contingent" truth we may take "It rains
to-day," or "The earth revolves round the sun." For neither one nor the
other of these is necessarily so. It is so as a matter of fact, but under
other circumstances it might have been otherwise. The contrary can be
conceived of and represented, and has in itself an equal degree of
possibility. Therefore such a fact requires to be and is capable of being
reasoned out. I can and must ask, "How does it happen that it rains
to-day? What are the reasons for it?" But as we must seek for sufficient
reasons for "contingent" truths, that is, for those of which the contrary
was equally possible, so assuredly we must seek for sufficient causes for
"contingent" phenomena and events, those which can be thought of as not
existing, or as existing in a different form. For these we must find
causes and actual reasons. Otherwise they have no foundation. The element
of "contingency" must be done away with; they must be shown to result from
sufficient causes. That is to say nothing less than that they must be
traced back to some necessity. For it is one of the curious fundamental
convictions of our reason, and one in which all scientific investigation
has its ultimate roots, that what is "contingent" is only apparently so,
and in reality is in some way or other based on necessity. Therefore
reason seeks causes for everything.

The search for causes involves showing that a thing was necessary. And
this must obviously apply to the world as a whole. If it were quite
obvious that the world and its existence as it is were necessary, that is,
that it would be contrary to reason to think of the world, and its
phenomena, and their obedience to law as non-existent, or as different
from what they are, all inquiry would be at an end. This would be _the_
ultimate necessity in which all the apparent contingency of isolated
phenomena and existences was firmly based. But this is far from being the
case. That anything exists, and that the world exists, is for us
absolutely the greatest "contingency" of all, and in regard to it we can
and must continually ask, "Why does anything exist at all, and why should
it not rather be non-existent?" Indeed, all our quest for sufficient
causes here reaches its