Rules of Syllogisms:

1. I hope all of you prefer to solve syllogs with the help of venn diagrams!

2. Direct relations which are given in the question, will always hold true. Thus if in the statement you’re given ‘All cats are rats.’ and in the conclusion too you’re given ‘All cats are rats.’ – it is true!

3. Thus, any contradiction to a direct relation, will always be wrong.
If statement is ‘Some scooters fly.’, and in conclusion you have, ‘Some scooters do not fly.’ – the conclusion is wrong. Contradiction of direct relation.

4. But if the contradiction to a direct relation is coupled with the word ‘possibility’, then the conclusion will be correct.

‘There is a possibility that some scooters do not fly.’ – is correct.

{Standard Rule: Where with any conclusion which is directly coming from the statements, the word ‘possibility’ is added, many a times the conclusion, which otherwise is wrong, will becomes correct.}

5. If in the statements given, relation is not made between two elements, then any direct relational conclusion between such elements will be wrong.

Cats are rats. Bats are Dogs. – is the statement.
Some rats are dog. – is the conclusion. And it is wrong.

Is there any connection between rats/cats with bats/dogs, that we can understand from the statement?

No! Hence, the direct relation in the conclusion is wrong.

But if the word possibility is added, then, ‘Some rats being dogs is a possibility.’ becomes correct!

6. And where direct relation exists, then adding the word ‘possibility’ is wrong.

Statement – All Apples are Bad.
Conclusion – All apples being bad is a possibility. – is wrong, as in the direct relation it is given that all apples are bad!

7. Either/Or condition:
When all the under mentioned 3 conditions follow cumulatively, only then will either/or option follow.

(i) One conclusion is +ve and one is –ve.
(ii) The elements are same in both the options.
(iii) Individually both conclusions must be wrong.
 
Check this out – Statements – No truck is rover. All rovers are land.
Conclusion – I. No land is truck.
II. Some land is truck.

Does this question satisfy all three conditions? Let’s check!
(i) Condition (1) - +ve and –ve?
Yes, it follows, as I (‘No land’) is –ve and II is = ve (‘some land’).
 
(ii) Condition (2) – elements in both conclusions to be same?
Yes, in both conclusions we have land and truck!

(iii) Condition (3) – both conclusions to be individually wrong?
Yes.
Conclusion I is wrong because there is no direct relation to that effect in the statement, and hence such a direct relation (no land is truck) of the conclusion will become wrong!

Conclusion II is wrong because there is no direct relation to that effect in the statement, and hence such a direct relation (some land is truck) of the conclusion will again become wrong!

{Please note , if in both the conclusions the word ‘possibility’ was added then they would have become correct!}