…logic treats of the reference of symbols in general to their objects.
…Logic is the study of the laws of signs so far as these denote things – those laws of signs which determine what things they denote and what they do not…
Logic treats of signs. A sign is a third.
Logic is a critic. It distinguishes between what it approves and what it condemns. This is why it must divide propositions by dichotomy.
Logic and metaphysics make no special observations; but they rest upon observations which have been made by common men. Metaphysics rests upon observations of real objects, while logic rests upon observations of real facts about mental products, such as that, not merely according to some arbitrary hypothesis, but in every possible case, every proposition has a denial, that every proposition concerns some objects of common experience of the deliverer and the interpreter, that it applies to that some idea of familiar elements abstracted from the occasions of the excitation, and that it represents that an occult compulsion not within the deliverer’s control unites that idea to those objects. All these are results of common observation, though they are put into scientific and uncommon groupings.
Logic, in its general sense, is, as I believe I have shown, only another name for semiotic (σημειωτική), the quasi-necessary, or formal, doctrine of signs.
Logic is a branch of philosophy. That is to say it is an experiential, or positive science, but a science which rests on no special observations, made by special observational means, but on phenomena which lie open to the observation of every man, every day and hour. There are two main branches of philosophy, Logic, or the philosophy of thought, and Metaphysics, or the philosophy of being.
Logic is the science of the general necessary laws of Signs and especially of Symbols.
It is pretty generally admitted that logic is a normative science, that is to say, it not only lays down rules which ought to be, but need not be followed; but it is the analysis of the conditions of attainment of something of which purpose is an essential ingredient. It is, therefore, closely related to an art; from which, however, it differs markedly in that its primary interest lies in understanding those conditions, and only secondarily in aiding the accomplishment of the purpose. Its business is analysis, or, as some writers prefer to say, definition.
At the outset, we define the principal purpose of logic to be to learn how to conduct any inquiry. [—]
In my opinion, the purpose of logic must ultimately come to be recognized as that of studying all that will be true of signs, or representations, independently of what particular signs have actually been created.
…logic is the science of regulating your thoughts so as not to be surprised when it can be avoided; and therefore whatever is said in logic about the modes of being of qualities, of laws, etc must be understood as regulative truth in Kant’s sense.
Now it may be that logic ought to be the science of Thirdness in general. But as I have studied it, it is simply the science of what must be and ought to be true representation, so far as representation can be known without any gathering of special facts beyond our ordinary daily life. It is, in short, the philosophy of representation.
The ultimate purpose of the logician is to make out the theory of how knowledge is advanced.
Supposing […] that normative science divides into esthetics, ethics, and logic, then it is easily perceived, from my standpoint, that this division is governed by the three categories. For Normative Science in general being the science of the laws of conformity of things to ends, esthetics considers those things whose ends are to embody qualities of feeling, ethics those things whose ends lie in action, and logic those things whose end is to represent something.
Logic is the theory of self-controlled, or deliberate, thought; and as such, must appeal to ethics for its principles. It also depends upon phenomenology and upon mathematics. All thought being performed by means of signs, logic may be regarded as the science of the general laws of signs.
Logic is that branch of normative science which studies the conditions of truth, or that kind of excellence which may or may not belong to objects considered as representing real objects.
…logic, as a normative science, entirely disregards what the particular state of things may be, and undertakes [to] show what procedure must lead to the discovery of truth, whatever that truth may be.
Logic, for me, is the study of the essential conditions to which signs must conform in order to function as such. How the constitution of the human mind may compel men to think is not the question; and the appeal to language appears to me to be no better than an unsatisfactory method of ascertaining psychological facts that are of no relevancy to logic.
Logic is the study of the essential nature of signs.
Logic, – I do not mean to define, but only to characterize it, – is supposed to be a science which investigates the principles upon which we are to decide whether any given argument makes its pretensions good or not.
Logic is no doubt a science of “thought”; but “thought,” in that sense, is no more internal than it is external. Logic is the science of truth and falsity. But truth and falsity belong as much to propositions printed in books as to propositions in the human consciousness. The fact that a proposition is conscious or unconscious does not affect its truth or falsity.
But it may be said that logic is the theory of reasoning, and that reasoning can only be performed by a mind. That is certainly true, and must be true; for if anything could independently reason, it would be what we understand by a mind. But it does not follow that the phenomena that psychologists discover have any bearing upon the theory of reasoning. [—]
Logic includes a study of reasoning, it is true, and reasoning may be regarded,-not quite correctly, but we may waive that point, – as a psychical process. If we are to admit that, however, we must say that logic is not an all round study of reasoning, but only of the conditions of reasoning being bad or good, and if good to what degree, and in what application. Now good reasoning is reasoning which attains its purpose. Its purpose is to supply a guide for conduct, – and thinking, being an active operation, is a species of conduct, – in case no percept from which a judgment could have been directly formed, is at hand. Its object is to say what the reasoner either will think when that percept occurs, or what he would think if it did occur. The psychological process of reasoning is wholly aside from the purpose of logic.
…it would seem proper that in the present state of knowledge logic should be regarded as coëxtensive with General Semeiotic, the a priori theory of signs.
The purpose and utility of logic […] lies in its final achievement of a methodeutic for the guidance of thought; and from this point of view logic is the theory of the self-control of thought in order to realize its intention, which is truth. So regarded, logic may be called a special kind of ethics, if by ethics we mean the theory of the self-control of conduct in order to realize a deliberately adopted purpose. For inquiry is only a particular kind of conduct.
In short, logic is the theory of all reasoning, while mathematics is the practice of a particular kind of reasoning.
Logic is the science of the classification of arguments. Reasoning is self-controlled thought; and thus Logic is directly dependent upon Ethics, or the science of self-control, in general.
Logic is […] synonymous with semeiotic, the pure theory of signs in general.
Logic, in general, seems to be the science of what is universally true respecting scientific representations. In a narrow sense, logic is the science of the general conditions of the truth of scientific representations.