ABSTRACT
Logic is the study of the general conditions of valid inference. An inference is an inferred judgment, that is, a judgment derived from another judgment, or from other judgments. All knowledge and all beliefs consist of judgments. Careful thinkers usually endeavour to make their inferences both valid and true; but it is possible for inferences to be valid without being true, or to be true without being valid. Logic is concerned with the general conditions of valid inference. Every actual argument relates to some particular problem mathematical or astronomical, physical or chemical, political or economic, and legal or moral. The full consideration of an argument must consequently take into account its special subject-matter, and requires a knowledge of it. The main aim of Logic is not to teach people to reason correctly, but to explain what happens when they do reason correctly, and why some reasoning is not correct.
