44. Nevertheless, objective certainty or determination does not bring about the necessity of the determinate truth. All philosophers acknowledge this, asserting that the truth of contingent futurities is determinate, and that nevertheless they remain contingent. The thing indeed would imply no contradiction in itself if the effect did not follow; and therein lies contingency. The better to understand this point, we must take into account that there are two great principles of our arguments. The one is the principle of _contradiction_, stating that of two contradictory propositions the one is true, the other false; the other principle is that of the _determinant reason_: it states that nothing ever comes to pass without there being a cause or at least a reason determining it, that is, something to give an _a priori_ reason why it is existent rather than non-existent, and in this wise rather than in any other. This great principle holds for all events, and a contrary instance will never be supplied: and although more often than not we are insufficiently [148] acquainted with these determinant reasons, we perceive nevertheless that there are such. Were it not for this great principle we could never prove the existence of God, and we should lose an infinitude of very just and very profitable arguments whereof it is the foundation; moreover, it suffers no exception, for otherwise its force would be weakened. Besides, nothing is so weak as those systems where all is unsteady and full of exceptions. That fault cannot be laid to the charge of the system I approve, where everything happens in accordance with general rules that at most are mutually restrictive.