DSC -- 1sr paper

Unit -- 2

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Topic:- Opposition of propositions

Opposition of proposition is the relation between two propositions which have the same subject and same predicate, but which differ either in quality or in quantity or in both.

For example --

A -- All men are mortal

E -- No men are mortal

In term logic the square of opposition of proposition is representing relations between the four basic categorical proposition.

As it is shown by use of the square, there can be four kinds of opposition of proposition.

(1) Contrary opposition,

(2) Sub- Contrary opposition.

(3) Contradictory opposition.

(4) Sub - altern opposition.

(1) Contrary opposition ---

Contrary opposition is a kind of opposition that holds between two universal propositions having the same subject and same predicate, but differing only in quality. Thus, 'A' and 'E' propositions are contrarily related.

For example ---

A -- All poets are emotional .

E -- No poets are emotional .

(2). Sub- Contrary opposition ------

Sub--Contrary opposition is a kind of opposition holding between two particular impositions having the same subject and same predicate but differing only in quality. Thus 'I' and 'O' propositions are Sub- contrarily related.

For example ----

I -- some flowers are white

O -- Some flowers are not white.

(3). Contradictory opposition ---

This kind of opposition obtains between two propositions having the same subject and same predicate, but differing both in quality and as well as in quantity. Thus, the pair, 'A' and 'O' is Contradictorily related. Similarly, 'E' and 'I' also contradictorily related.

For example ---

A -- All judges are lawyers

O -- Some judges are not lawyers.

and

E -- No men are perfect

I -- Some men are perfect

(4) Sub- altern opposition ---

Sub-altern opposition is a kind of opposition between two propositions having the same subject and same predicate. that have the same quality, but differ in quantity. This opposition holds between a Universal proposition and its corresponding particular proposition. This opposition obtains between 'A' and 'I' propositions as well as between "E' and "O' propositions.

For example ---

A --. All men are mortal

I -- Some men are mortal.

And

E --. No men are perfect

O -- Some men are not perfect.

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