One of the most original developments of Croce's thought--a doctrine that does not owe its validity only to its connection with the system, since we can find it adumbrated already in such widely divergent philosophies as those of Socrates and Thomas Aquinas, of Descartes and Rosmini, but which in Croce's system acquires a new and wider meaning--is the theory of the practical origin of theoretical error, which we shall briefly discuss in this chapter. From a strictly logical standpoint, every error is mere privation or negativity, the opposite of the logical value which is truth, and therefore inexistent outside the moment of opposition. As there are not two values in æsthetics, the beautiful and the ugly, but one only, beauty or expression, of which ugliness or non-expression is merely the negative aspect, so in logic also there is but one value, thought or truth, and error is non-thought, that which logically has no being or reality. There is no thought which is not a thinking of truth. Let us pause for one instant to consider this last proposition, which at first sight undoubtedly has a somewhat paradoxical air. And yet it is impossible not to accept it, unless we are willing to fall into the most radical scepticism, which would imply a renunciation not only of every form of thought, but even, since there is no action which is not founded on knowledge, of every kind of action. If we believed that it were possible for our thought to think that which is not true, no external criterion or standard of truth could even be substituted for that which thought intrinsically would lack, since the apprehension of such external standards would in itself be an act of thought, and therefore suffer from the indetermination and uncertainty of thought itself. This belief in the validity of human thought is in fact, however disguised or even openly denied, present in every thinking and acting being: every thought, every action of man is an implicit declaration of this faith. And once we have consciously acquired it, as an inalienable, intrinsic characteristic of our whole spiritual activity, it is evident that it leaves no place for faith as such, for an obscure, independent faculty, a mystical intuition, different from and superior to our human thought, and which could mysteriously endow thought itself with the gratuitous gift of truth.