This article is about the systematic study of the form of arguments. A valid inference is one where there is a specific relation of logical support between the assumptions of the inference and its conclusion. In ordinary discourse, inferences may be signified by words like logic gates project for class 12 pdf, hence, ergo and so on.

Upon this first, and in one sense this sole, rule of reason, that in order to learn you must desire to learn, and in so desiring not be satisfied with what you already incline to think, there follows one corollary which itself deserves to be inscribed upon every wall of the city of philosophy: Do not block the way of inquiry. The concept of logical form is central to logic. The validity of an argument is determined by its logical form, not by its content.

Traditional Aristotelian syllogistic logic and modern symbolic logic are examples of formal logic. Informal logic is the study of natural language arguments.

The study of fallacies is an important branch of informal logic. Since much informal argument is not strictly speaking deductive, on some conceptions of logic, informal logic is not logic at all. Formal logic is the study of inference with purely formal content.

An inference possesses a purely formal content if it can be expressed as a particular application of a wholly abstract rule, that is, a rule that is not about any particular thing or property. The works of Aristotle contain the earliest known formal study of logic. Modern formal logic follows and expands on Aristotle.

In many definitions of logic, logical inference and inference with purely formal content are the same. This does not render the notion of informal logic vacuous, because no formal logic captures all of the nuances of natural language. Symbolic logic is the study of symbolic abstractions that capture the formal features of logical inference.

Symbolic logic is often divided into two main branches: propositional logic and predicate logic. Mathematical logic is an extension of symbolic logic into other areas, in particular to the study of model theory, proof theory, set theory, and recursion theory. However, agreement on what logic is has remained elusive, and although the field of universal logic has studied the common structure of logics, in 2007 Mossakowski et al. Logic is generally considered formal when it analyzes and represents the form of any valid argument type.

The form of an argument is displayed by representing its sentences in the formal grammar and symbolism of a logical language to make its content usable in formal inference. Simply put, formalising simply means translating English sentences into the language of logic. This is called showing the logical form of the argument. It is necessary because indicative sentences of ordinary language show a considerable variety of form and complexity that makes their use in inference impractical.

Second, certain parts of the sentence must be replaced with schematic letters. Thus, for example, the expression “all Ps are Qs” shows the logical form common to the sentences “all men are mortals”, “all cats are carnivores”, “all Greeks are philosophers”, and so on. A indicates the judgement ‘all – are -‘.