OUTLINE OF CONTENTS
1. WHAT IS
“LOGIC “
2. PROPOSITION
3. DIFFERENCES
BETWEEN PROPOSITION AND SENTENCE
4. PREMISS
5. CONCLUSION
6. ARGUMENT
7. INFERENCE
8. VALIDITY
AND INVALIDITY
9. DEDUCTIVE
AND INDUCTIVE ARGUMENTS
10. SOUND
ARGUMENT
11. ATOMIC
ARGUMENT
12. PREMISS
AND CONCLUSION INDICATORS
13. LAWS OF
THOUGHT
14. IMPORTANCE OF LOGIC 1. What is Logic?
According to ‘Irvin Copi’ – Logic is the study of the methods and principles used to distinguish good (correct) reasoning from bad (incorrect) reasoning.
2. Define ‘Proposition’
A proposition is a ‘declarative statement’ that asserts or says something about a subject (e.g.) Ola is a man.
3. The differences between ‘proposition’ and ‘sentence’
i. A sentence has a wider range, as it could be an ‘exclamation’, a ‘command’ or a ‘question’. ‘But’ – A proposition is only a ‘declarative statement’ that is asserting something. For example:-
A sentence could be:-
§ ‘Oh! I feel so tired’. - Exclamation
§ ‘Hey! Come over here’. - Command
§ ‘What do you want’? - Question
A proposition is simply:-
§ Yoruba’s are Nigerians – Declarative statement
ii. Two or more different sentences could be conveying only one proposition. For example;
§ God is kind - English
§ Oluwa dara - Yoruba (3 sentences)
§ Chineke idinma - Igbo
But only one proposition (factual statement) is contained within all three i.e. ‘Benevolence is a characteristic nature of God’.
iii. Sentences and propositions could have relative truth values, as they could either be;
§ Same sentence but different propositional truth values
For example;
§ The sentence, “Olusegun Obasanjo” is the Nigerian President when uttered in 2004 asserts a true proposition but, when uttered in 2011 asserts a false proposition.
§ Different sentence but same propositional truth value.
For example;
§ If one says, ‘I am hungry’ and another says, ‘You urgently desire to eat’; both sentences though different assert the same proposition (either both true or both false).
4. Define ‘Premiss’
Premiss (es) is a proposition or those propositions that are said to provide evidences or reasons for reaching and accepting a final judgment in an argument.
5. Define ‘conclusion’
A conclusion is that single proposition which is finally affirmed as a last judgment, on the basis of some other propositions in an argument.
6. Define ‘argument’
An argument is any collection of propositions of which they derive systematically from one another in order to arrive at a final judgment. It contains premisses and a conclusion.
For example, an Argument is;
§ All automobiles have fuel engines – Premiss 1
§ Lamborghini car is an automobile - Premiss 2
§ So, Lamborghini car has a fuel engine - Conclusion
7. Define ‘inference’
Inference is the psychological or mental process, used in the course of an argument, by which the premisses derive from one another in order to arrive at the conclusion.
8. Validity And Invalidity
The terms ‘valid’ and ‘invalid’ are used to describe only ‘deductive arguments’. Therefore;
§ A ‘valid’ deductive argument is an argument that can never have ‘true premisses and false conclusion’.
§ An ‘invalid’ deductive argument is an argument that may not have ‘false premisses and true conclusion’.
9. Deductive And Inductive Arguments
A deductive argument is one, in which the/its conclusion follows of ‘necessity’ from its premisses; also this necessity is ‘not’ a matter of degree and does ‘not’ depend on what else may be the case.
A deductive argument can progress from;
§ General to particular instances
§ General to General instances
§ Particular to particular instances
Example of a deductive argument (general to particular) goes thus;
All fishes are reptiles
Shark is a fish
So, shark is a reptile
An inductive argument is one, in which the /its conclusion follows from its premisses based on ‘probability’; also this probability ‘is’ a matter of degree and ‘depends’ on what else may be the case.
An inductive argument can progress from:-
§ Particular to General instances
§ Particular to Particular instances
§ General to General instances
Example of an inductive argument (particular to general) goes thus;
Beans is a proteinous meal
Egg is a proteinous meal
Beef is a proteinous meal
Moi-Moi is a proteinous meal
Milk toast is a proteinous meal
Cheese is a proteinous meal
Probably, all meals are proteinous
10. Sound Argument
A sound argument is a ‘valid deductive argument’ whose propositions (premisses and conclusion) are all true. For example:
All women are humans
All human are mammals
So, all women are mammals
11. Atomic Argument
An atomic argument is a simple argument, which is made up of one premises and a conclusion that follows directly from it. For example;
I think
Therefore, I exist
12. Premiss And Conclusion Indicators
These refer to those special words and expressions used to point out (identify) premisses and conclusion (respectively) in an argument.
§ Examples of premises indicators are;
‘Because’; ‘for’; ‘since’; ‘as’; ‘but’; and so on
§ Examples of conclusion indicators are;
‘So’; ‘therefore’; ‘thus’; ‘consequently’; ‘Hence’; ‘accordingly’; ‘for these reasons’; and so on
13. The laws of thought (a.k.a. principles of thought)
In logic, there are three (3) laws/principles of thought. These are:
§ The law of ‘identity’
§ The law of ‘contradiction or non contradiction’
§ The law of ‘excluded middle’
i. The law of identity
States that, ‘if anything is p, then it is p’ meaning that, if a proposition is true, then it is true, fixed and unchanged. If otherwise, the law of identity ceases to operate. For example;
‘Nigeria gained independence in the year 1960’.
ii. The law of contradiction or non contradiction
States that, ‘nothing can be both, p and not p’ meaning that, a statement cannot be true and false at the same time. Therefore, a contradiction is false. For example;
‘Edward is human and not human; is false’.
Or
‘Edward cannot be, human and not human at the same time?
iii. The law of excluded middle
States that, ‘any thing must be either p or not p’ implying that, any proposition is either true or false. So, any thing must have a particular quality. E.g. ‘God either exists or does not exist’.
14. The Importance Of Logic
i. It helps to avoid fallacious reasoning.
ii. It serves as a tool for philosophical enquiry.
iii. It helps to critically evaluate sensitive issues.
iv. It aids in the promotion of social and legal justice.
v. It helps one to develop sound and cogent argument.
vi. It helps in advancing scientific research.
vii. It illuminates all branches of human knowledge.
viii. It helps to rightly analyze issues of reason and faith.
