Everybody has a positive intellectual certainty that a complicated order cannot be the result of accident, and that for every event there must be a cause, though not every one will be able readily to demonstrate the truth of his certainty. But if the philosopher should look for the proof, he would do so in no other way than by reflecting upon his natural and direct knowledge, and by trying to become conscious of what he has thus directly found out. To illustrate by a few examples: We are all convinced of the existence of an exterior world, and any one who is not an idealist will call this conviction a reasonable certainty, and yet only a few will be able to answer the subtle questions of a sceptic. This certainty again is a natural but not a scientific one. How difficult it is here also for reason to attain scientific certainty, how easy it is to go astray in these researches, is proved by the errors of idealism so incomprehensible to the untrained natural mind. Let us ask, finally, any one: Why must we say: “_Cæsar_ defeated _Pompey_,” but not “_Cæsar_ defeated of _Pompey_”? He will tell us this is nonsense; maybe he will add that the genitive has another meaning. But should I ask further how the meaning of the genitive differs from that of the accusative, as both cases seem to have often the same meaning, I shall get no answer. There is a certitude, but only a natural one. Even if I should ask modern students of the psychology and history of languages, like _Wundt_, _Paul_, or whatever their names may be, I should not get a satisfactory answer either. The whole logic of language, with its subtle forms and moods of expression—how difficult for scientific research! And yet the mind of even a child penetrates it, and not only a European child, but the Patagonian and negro child, who is able to master by its intellectual power complex languages, with four numbers, many moods, fourteen tenses, etc.