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Logic is a normative science; that is to say, it is a science of what is requisite in order to attain a certain aim. That does not prevent its being purely theoretical although it will be intimately connected with an art. For the normative science does not necessarily inquire how we are to act in order to pursue a purpose, or to what our efforts ought to be directed; but simply considers what conditions, whether they be voluntarily or involuntarily fulfilled, have to be satisfied. At the same time, it may naturally be expected that an art should be capable of being built upon the foundations of a normative science. In all that, there seems, at present to be a tolerable agreement, today. But one is surprised to find how much room for different