Definition of Logic
Logic (definition) is the art/science of good reasoning (arguments or inferences). Reasoning is a species or kind of thinking that aims at a conclusion. Thus good reasoning is thinking well that aims at a conclusion.(Aristotle: A horse is an animal. Therefore the head of a horse is the head of an animal.) Thus Logic is the study of arguments. More specifically, logic is the study of the criteria for distinguishing good arguments from bad arguments.
We will be mainly concerned with deductive arguments. A deductive argument is an argument whose premises claim to provide conclusive grounds for the truth of its conclusion. In a deductive argument, if in fact the premises do not provide conclusive grounds (impossible for the premises to be true and the conclusion false) for the conclusion, then the argument is invalid; it the premises do provide conclusions grounds for the conclusion, then the argument is valid. Every deductive argument is either valid or invalid. We will study two theories of deduction: Aristotle's theory and modern symbolic logic's theory of deduction. The purpose of a theory of deduction is to explain or givean account of the relationship between the premises and the conclusion of a valid deductive argument. We will particularly be concerned with different methods for evaluating deductive arguments: namely, distinguishing between valid and invalid arguments.