On Reason by Baruch Spinoza

At present we have to inquire why it happens that sometimes, although we see that a certain thing is good or bad, we nevertheless do not find in us the power either to do the good or to abstain from the bad, and sometimes, however, we do indeed [find this power in us]. This we can easily understand if we consider the causes that we assigned to opinions, which we stated to be the causes of all affects. These, we then said, [arise] either from hearsay, or from experience. And since all that we find in ourselves has greater power over us than that which comes to us from outside, it certainly follows that Reason can be the cause of the extinction of opinions which we have got from hearsay only (and this is so because reason has not like these come to us from outside), but by no means of those which we have got from experience. For the power which the thing itself gives us is always greater than that which we obtain by way of consequence through a second thing; we noted this difference when speaking of reasoning and of clear understanding, and we did so with the Rule of Three as an illustration. For more power comes to us from the understanding of proportion itself, than from the understanding of the rule of proportion. And it is for this reason that we have said so often that one love may be extinguished by another which is greater, because in saying this we do not, by any means, intend to refer to desire which does not, like love, come from true knowledge, but comes from opinion.