Having learnt from experiment and argument that a stone falls downwards, a man indubitably believes this, and always expects the law he has learnt to be fulfilled.But learning just as certainly that his will is subject to laws, he does not and cannot believe it.However often experiment and reasoning may show a man that under the same conditions and with the same character he will do the same thing as before, yet when, under the same conditions and with the same character, he approaches for the thousandth time the action that always ends in the same way, he feels as certainly convinced as before the experiment that he can act as he pleases. Every man, savage or sage, however incontestably reason and experiment may prove to him that it is impossible to imagine two different courses of action in precisely the same conditions, feels that without this irrational conception (which constitutes the essence of freedom) he cannot imagine life. He feels that, however impossible it may be, it is so, for without this conceptions of freedom not only would he be unable to understand life, but he would be unable to live for a single moment.He could not live, because all man's efforts, all his impulses to life, are only efforts to increase freedom. Wealth and poverty, fame and obscurity, power and subordination, strength and weakness, health and disease, culture and ignorance, work and leisure, repletion and hunger, virtue and vice, are only greater or lesser degrees of freedom.A man having no freedom cannot be conceived of except as deprived of life.If the conception of freedom appears to reason a senseless contradiction, like the possibility of performing two actions at one and the same instant of time, or of an effect without a cause, that only proves that consciousness is not subject to reason.

~ Leo Tolstoy

Even as to himself, a man cannot pretend to know what he is in himself from the knowledge he has by internal sensation. For as he does not as it were create himself, and does not come by the conception of himself a priori but empirically, it naturally follows that he can obtain his knowledge even of himself only by the inner sense, and consequently only through the appearances of his nature and the way in which his consciousness is affected. At the same time, beyond these characteristics of his own subject, made up of mere appearances, he must necessarily suppose something else as their basis, namely, his ego, whatever its characteristics in itself may be... Now man really finds in himself a faculty by which he distinguishes himself from everything else, even from himself as affected by objects, and that is reason. This being pure spontaneity is even elevated above the understanding. For although the latter is a spontaneity and does not, like sense, merely contain intuitions that arise when we are affected by things (and are therefore passive), yet it cannot produce from its activity any other conceptions than those which merely serve to bring the intuitions of sense under rules, and thereby to unite them in one consciousness, and without this use of the sensibility it could not think at all; whereas, on the contrary, reason shows so pure a spontaneity in the case of what I call ideas [Ideal Conceptions] that it thereby far transcends everything that the sensibility can give it, and exhibits its most important function in distinguishing the world of sense from that of understanding, and thereby prescribing the limits of the understanding itself.

~ Immanuel Kant