INTRODUCTION TO LOGIC

 . . this we do affirm—that if truth is to be sought in every division of Philosophy, we must, before all else, possess trustworthy principles and methods for the discernment of truth. Now the Logical branch is that which includes the theory of criteria and of proofs; so it is with this that we ought to make our beginnings.

—Sextus Empiricus

. . . bad reasoning as well as good reasoning is possible; and this fact is the foundation of the practical side of logic.

—Charles Sanders Peirce

What is logic?

Logic is the study of the methods and principles used to distinguish good (correct) from bad (incorrect) reasoning. 

traditional part of the study of logic has been the examination and analysis of falacies, which are common and often quite "natural" mistakes in reasoning. 

study of logic will give students techniques and methods for testing the correctness of many different kinds of reasoning

Logic has frequently been defined as the science of the laws of thought.

All reasoning is thinking, but not all thinking is reasoning

Premisses and Conclusions

Inference is a process by which one proposition is arrived at and affirmed on the basis of one or more other propositions accepted as the starting point of the process are either true or false, and in this they differ from questions, commands, and exclamations. 

We use the term "proposition" to refer to what such sentences as these are typically uttered to assert

 Corresponding to every possible inference is an argument, and it is with arguments that logic is chiefly concerned.