Logic is one of the major branches of philosophy, which is commonly understood as the science or study of correct processes of thinking or reasoning. Broadly construed, logic, therefore, is that specific branch of philosophy that studies the processes of correct thinking.
Etymologically speaking, the term “logic” is derived from the Greek word logos, which is often translated in English as “word”, “discourse” or “reason”. In the Greek tradition of understanding the nature of reality, the term “reason” was commonly appropriated. And for the ancient Greek thinkers, logos as “reason” could mean two things, namely: 1) that which refers to “human reason”, which seeks to attain an objective or universal understanding of the nature of reality, and 2) that which refers to “universal intelligence” or “rational divine intelligence”―indeed, that universal ruling force that governs the cosmos.
When understood in the second sense, logos then means (as the ancient Greek thinkers would have us believe) the “light-giving principle”, which enables human persons to understand the nature, dynamics, and mysteries of the universe. When understood in the first sense, that is, as “human reason”, logos connotes “study”, that is, the rationality of the human mind which seeks to attain an objective or universal understanding of the nature of reality.
Thus, when we employ the term logos in our attempt to make sense of or study something, then we are dealing with the term logos in the first sense. For example, when we define the term “psychology” from the vantage point of its etymology, then we say that psychology comes from the two Greek words, namely, psyche, which means “mind”, and logos, which means “study”. Thus, etymologically speaking, psychology is defined as the study of the mind. Indeed, it is in this context that “logic” is, again, defined as the study (or science or reason) of the correct processes of thinking or reasoning.
More specifically, when we study the correct processes of thinking or reasoning, we are necessarily dealing with arguments.
Hence, in logic, we will be primarily dealing with the principles that govern the validity of arguments, that is, whether a certain conclusion follows from the given premises or assumptions.
Let us consider the examples below.
If it rains today, then the road is wet.
It rains today.
Therefore, the road is wet.
All men are mortal.
Socrates is a man.
Therefore, Socrates is mortal.
The professor will be absent if and only if she is sick.
The professor is sick.
Therefore, she will be absent.
The arguments above are obviously valid arguments because their conclusions necessarily follow from the premises. Again, if the premises are true, then the conclusion must be true for the argument to be valid. However, there are more complicated arguments whose validity cannot be determined by simply looking at them. These arguments require a thorough analysis before we can say that they are indeed valid or not. This is precisely what concerns us in logic, and this is what the rest of the discussions in logic would like to address.