All applied logic, inductive as well as deductive, is based on formal logic, and this in turn on the “laws of thought,” or rather of thinking. These are strictly regulative or abstract, and differ altogether from the natural laws of thought, such as those of similarity, contiguity and harmony, as well as from the rules of applied logic, such as those of agreement and difference. The fundamental laws of thinking are three in number, and their bearing on all the higher questions of religious philosophy is so immediate that their consideration becomes of the last moment in such a study as this. They are called the laws of Determination, Limitation and Excluded Middle. The first affirms that every object thought about must be conceived as itself, and not as some other thing. “A is A,” or “_x_ = _x_,” is its formal expression. This teaches us that whatever we think of, must be thought as one or a unity. It is important, however, to note that this does not mean a mathematical unit, but a logical one, that is, identity and not contrast. So true is this that in mathematical logic the only value which can satisfy the formula is a concept which does not admit of increase, to wit, a Universal. From this necessity of conceiving a thought under unity has arisen the interesting tendency, so frequently observable even in early times, to speak of the universe as one whole, the το παν of the Greek philosophers; and also the monotheistic leaning of all thinkers, no matter what their creed, who have attained very general conceptions. Furthermore, the strong liability of confounding this speculative or logical unity with the concrete notion of individuality, or mathematical unity, has been, as I shall show hereafter, a fruitful source of error in both religious and metaphysical theories. Pure logic deals with quality only, not with quantity. The second law is that of Limitation. As the first is sometimes called that of Affirmation, so this is called that of Negation. It prescribes that a thing is not that which it is not. Its formula is, “A is not not-A.” If this seems trivial, it is because it is so familiar. These two laws are two aspects of the same law. The old maxim is, _omnis determinatio est negatio_; a quality can rise into cognition only by being limited by that which it is not. It is not a comparison of two thoughts, however, nor does it limit the quality itself. For the negative is not a thought, and the quality is not _in suo genere finita_, to use an expression of the old logicians; it is limited not by itself but by that which it is not. These are not idle distinctions, as will soon appear.