The word logic is basic structure of good reasoning. The word logic is derived from the Greek logos, which means study, word or discourse. It deals with the nature of arguments, that is, the word logic is basic structure of good reasoning. Logic is the study of the criteria of differentiating correct from incorrect arguments. Argument on the other hand is a group of propositions which makes claim about something. For a proposition to qualify as an argument, it must have premise(s) and conclusion. Argument can also either be deductive or inductive. Deductive argument is that which the conclusion follows from its premises with absolute necessity or certainty. Deduction moves from general to the specific that is, deducing from a proposition describing a condition that holds in all instances to a particular instance….
An argument can also be valid or invalid. Valid argument means that if the premises are true, then the conclusion must be true, that is, the premises logically imply the conclusion. It is impossible in a valid argument to have a false conclusion when all the premises are true. Invalid argument on the hand, means that, it is possible for the conclusion to be false even if the premise is true; here the premise does not entail the conclusion.
Examples of deductive argument are:
Premise 1: All women are mortal Premise 2: Bolanle is a woman Conclusion: Therefore Bolanle is mortal
Premise 1: Tamuno is an Agnostic
Conclusion: Therefore, Tamuno suspends judgment about the existence of God.
Premise 1: If John gets a raise, then he will buy a house
Premise 2: If John buys a house, he will run for a position on the neighbourhood council.
Conclusion: Therefore, if John gets a raise he will run for a position on the neighbourhood council.
These examples above are deductively valid, this is because the relationship between the premise and the conclusion is such that the truth of the premise guarantees the truth of the conclusion.
Inductive argument on the other hand is one in which the premise does not lead to the conclusion with certainty. Induction is based on probability. There are five degree of support identified by Thomas that a premise can give to a conclusion to make it probable or like. They are Nil, weak, moderate, strong and deductively valid. Example of an inductive argument:
Premise 1: Bruce gets drunk most of the time Premise 2: Yesterday he was drunk
Premise 3: Therefore, he will be drunk today.
Premise 1: Sule refuses to eat his food Conclusion: Therefore, he is not hungry
In the two arguments, the conclusion does not follow from the premise(s). In the first example, the fact that Bruce gets drunk most of the time, does not mean that we can conclude with certainty that Bruce will be drunk today, today may just be an exemption from his drunken habit. In the second example, even though hunger is one of the reasons, Sule may not have eaten his food. It is however not the only reason to have made such conclusion. Other reasons could be that Sule is sick, or maybe he is fasting. It could even be that he does not like the food offered to him. So these arguments are inductive because the support which the premise gives to the conclusion is weak.