Beginning of Essay
Logic is the science dealing with the principles of valid reasoning and argument. The study of logic is the effort to determine the conditions under which one is justified in passing from given statements, called premises, to a conclusion that is claimed to follow ....

Middle of Essay
.... of the argument, not on its content. If the argument were valid, some other term could be substituted for all occurrences of any one of those used and validity would not be affected. By substituting “four-footed” for “two-footed,” it can be seen that the premises could both be true and the conclusion false. Thus the argument is invalid, even though it has a true conclusion. Epistemology is the branch of philosophy that addresses the philosophical problems surrounding the theory of knowledge. Epistemology is concerned with the definition of knowledge and related concepts, the sources and criteria of knowledge, the kinds of knowledge possible ....