Logic is the science of thought as expressed in language. This means that the questions on logic are to be solved as per the information given without any concern of the formal validity or truth of the statements i.e. conclusion should follow directly from the statements given. Without this unique characteristics, the Logic test becomes an instrument of teaching the candidates to follow the rules and work as per the instructions without an error.
In Logic, any categorical statement is termed as the Proposition
A Proposition (or a categorical statement) is a statement that asserts that either a part of, or the whole of, one set of objects – the set identified by the subject term in the sentence expressing that statement – either is included in, or is excluded from, another set – the set is identified by the predicate term in that sentence.
The standard form of a proposition is:
Quantifier + Subject + Copula + Predicate
Thus the proposition consists of four parts:
1. Quantifier : The word “All” , “No” and “Some” are called Quantifiers because they specify a quantity. “All” and “No” are Universal Quantifiers as they refer to every object in a certain set, while the quantifier “Some” is a particular quantifier as it refers to at least one existing object in a certain set.
2. Subject (“S”) : The subject is that about which something is said.
3. Predicate (“P”) : It is the part of the proposition denoting that which is affirmed or denied about the subject.
4. Copula : The Copula is that part of the proposition which denotes the relation between the subject and the predicate.
Example : All Jokers are men.
Here : All -> Quantifier ; Jokers -> Subject ; Are-> Copula ; Men -> Predicate
Four Fold Classification of the Proposition
Propositions are classified in to four types
Universal Affirmative Proposition (denoted by “A”)
It distributes only the subject i.e. the predicate is not interchangeable with the subject while maintaining the validity of the proposition.
e.g. All cats are mammals.
This is proposition A since we cannot say “All mammals are cats.”
Universal Negative Proposition (denoted by “E”)
It distributes both the subject and the predicate i.e. an entire class of predicate term is denied to the entire class of the subject term, as in the proposition.
e.g No girl is beautiful.
Particular Affirmative Proposition (denoted by “I”)
It distributes neither the subject nor the predicate.
e.g Some men are foolish.
Here the subject term “Men” is used not for all but only for some and similarly the predicate term “foolish” is affirmed for a part of subject class. So both are undistributed.
Particular Negative Proposition (denoted by “O”)
It distributes only the predicate.
e.g Some animals are not domestic.
Here the subject term “animals” is used only for a part of its class and hence is undistributed while the predicate “wild” is denied in entirety to the subject term and hence is distributed.
Learning about classification helps to make logical deduction in the Competitive exams. How to deduce is explained in the next post. Do check.