Discussion Forum

In the following question, three statements are given followed by four conclusions numbered I,II,III and IV.You have to take the given statements to be true even if they seem to be at variance with commonly known facts and then decide which of the given conclusions logically follows from the given statements disregarding commonly known facts.

 Statements : All doors are buses. All buses are leaves. No leaf is a flower. 

Conclusion : I. No flower is a door. II. No flower is a bus. III. Some leaves are doors. IV. Some leaves are buses.

Answer:

Explanation:

IV is the converse of the second premise and so it holds.

All doors are buses, All buses are leaves.

Since both the premises are universal and affirmative, the conclusion must be universal affirmative and should not contain the middle term. So, it follows that 'All doors are leaves'. III is the converse of this conclusion and so it holds.

All buses are leaves. No leaf is a flower.

Since both the premises are universal and one premise is negative, the conclusion must be universal negative and should not contain the middle term. So, it follows that 'No bus is flower'. II is the converse of this conclusion and so it holds.

All doors are buses. No bus is flower.

As discussed above, it follows that 'No door is flower', I is the converse of this conclusion and so it also holds.