This limitation '_under certain conditions_' is the point to be noticed. All scientific laws are abstract laws; and there is no bridge over which to pass from the concrete to the abstract; just because the abstract is not a reality, but a form of thought, one of our, so to speak, abbreviated ways of thinking. And, although a knowledge of the laws may _light up_ our perception of reality, it cannot become _this perception itself_. Here we may agree with what Labriola justly felt, when, showing his dissatisfaction with the term _scientific socialism_, he suggested, though without giving any reasons, that that of _critical communism_ might be substituted.[63] If then from abstract laws and concepts we pass to observations of historical fact, we find, it is true, points of agreement between our ideals and real things, but at the same time we enter upon those difficult calculations and conjectures, from which it is always impossible to eliminate, as was remarked above, the diversity of opinions and propensities. In face of the future of society, in face of the path to be pursued, we have occasion to say with Faust--Who can say I believe? Who can say I do not believe? Not indeed that we wish to advocate or in any way justify a vulgar scepticism. But at the same time we need to be sensible of the relativity of our beliefs, and to come to a determination in practice where indetermination is an error. This is the point; and herein lie all the troubles of men of thought; and hence arises their practical impotence, which art has depicted in Hamlet. Neither shall we wish, in truth, to imitate that magistrate, famous for miles around the district where he officiated for the justice of his decisions, of whom Rabelais tells us, that he used the very simple method, when about to make up his mind, of offering a prayer to God and settling his decision by a game of odd and even.[64] But we must strive to attain personal conviction, and then bear always in mind that great characters in history have had the courage to _dare_. '_Alea jacta est_,' said Cæsar; '_Gott helfe mir, amen!_' said Luther. The brave deeds of history would not be brave if they had been accompanied by a clear foresight of the consequences, as in the case of the prophets and those inspired by God.