as well ask a blind man to make true or false judgments about the real effects of certain combinations of colors, as to ask either John or Thomas, defined as common sense defines them, to make any judgments about each other. Common sense will assert that a blind man can learn and repeat verbally correct statements about color, or verbally false statements about color, but, according to the common-sense view, in no case can he err about color-ideas as such, which are never present to him. You will be quite ready to say that a dog can make mistakes about the odors of the numberless tracks on the highway. You will assure us, however, that you cannot make mistakes about them because these odors do not exist for you. According to the common-sense view, a mathematician can make blunders in demonstrating the properties of equations. A Bushman cannot, for he can have no ideas corresponding to equations. But how then can John or Thomas make errors about each other, when neither is more present to the other than is color to the blind man, the odor of the tracks on the highway to the dog’s master, or the idea of an equation to a Bushman? Here common sense forsakes us, assuring us that there is such error, but refusing to define it.
The inconsistency involved in all this common-sense view, and the consequences of the inconsistency, will appear yet better with yet further illustration. A dream is false in so far as it contains the judgment that such and such things exist apart from us; but at least in so far as we merely assert in our dreams about the objects as we conceive them, we make true
