The study of the methods and principles of sound reasoning. The study of logic focuses on whether the process, by which the conclusion is derived from a set of initial assumptions (premises), is correct. It is not concerned with examining or determining the truth of the premises. Given true premises, the conclusion must be true if the process to derive the conclusion is correct. Here is an example:
Premise: A dictionary is a reference title.
Premise: Visual Mathematics Dictionary is a dictionary.
Conclusion: Hence, Visual Mathematics Dictionary is a reference title.
Here is another example:
Premise: All reference titles are English dictionaries.
Premise: Visual Mathematics Dictionary is a reference title.
Conclusion: Hence, Visual Mathematics Dictionary is an English dictionary.
As shown, the conclusion may not be correct if at least one of the premises (the first one in the second case) is wrong.