Deduction is the process through which we reach up to particular conclusion with the help of universal facts.
Or in other words, deduction is the process of drawing generalization, through a process of reasoning on the basis of certain assumptions which are either self-evident or based on observation. In deduction, we deduce generalizations from universal to particular. Deduction can give conclusive evidence. Depending upon the premises, every deductive reasoning is either valid or invalid.
The main task of deductive logic is to clarify the nature of relation between premises and conclusions in valid arguments. It is concerned with the working out of logical implications between propositions. Let us consider an example: All men are mortal. John is a man. John is mortal.