- The Etymological Definition of Logic
The term “logic” came from two Greek words “logos” which means discourse which is connected thought express in words logic therefore in the methods and principles which permit one to distinguish a correct reasoning from an incorrect one.
- Formal Definition of Logic
Briefly speaking, we might define logic as the study of the principle of correct reasoning or it is the science of the laws of thought which governs correct reasoning.
In the fourth century BC, the ancient Greek philosopher, Aristotle considered logic as an organon, that is an instrument which permits one to attain the truth in any discuss or argument in the course of thinking. The concern of logic is that of distinguishing correct reasoning from incorrect reasoning to the course of agreement.
- Truth and Validity
The logician main concern in an argument is that of finding out whether it is valid or invalid. But most often than not, some mixed up had been made by learners in logic, on the distinction between truth and validity. It should therefore be necessary by that some clarification be made on this at this initial stage.
In fact, validity and invalidity is attributed to an argument while truth and validity is attributed to a preposition. Hence, the premises is an argument can be considered as true or false, for they deal with the judgment of fact of content of a statement.
But an agreement is considered as either valid or invalid when it conforms to the rules of logic or forms of an argument. If in argument, the premises are true and the conclusion is likewise, then the argument is valid and, if the premises are true and the conclusion false, then the argument is invalid. Consequently, it is impossible for a valid argument to have true premises and a false conclusion.
Hence, it is illogical and incorrect to speak on a true argument (or syllogism) if it means a valid argument or if a valid premise or conclusion, if it means a true conclusion. In other words, arguments are neither true nor false.
- They can only be valid or invalid, just as proposition are neither valid nor invalid.
- They can only be neither true nor false.
- All women are females (True)
Susan is a woman (True)
Therefore, Susan is a female (True) and (Valid)
- All dogs are animals (true)
All cats are animals (True)
Therefore, all cats are dogs (False) and (invalid)
