Logical Reasoning – Deductive

Verbal Reasoning makes a substantial part of CAT and other MBA Exams Verbal Ability questions. Questions on Syllogism are very often asked in many MBA Entrance Examinations. Read to understand Syllogism.

Created On: Aug 2, 2013 17:40 IST

Logical consistency is another branch of Deductive Logic. A set of sentences is said to be consistent if and only if there is at least one possible situation in which they are all true. If two sentences cannot be both true at the same time, they are said to be contrary. For example, "I have exactly 10 fingers" and "I have exactly 9 fingers" are contrary (both statements cannot be true, but both could be false). Based on these we need to look at a few keywords that will help us solve these kinds of problems. Logical Consistency problems appear in CMAT, SNAP, XAT, MAT etc.

Logical Consistency questions have a main statement, one needs to identify what type of statement it is and find out which statement will follow logically.

• If/Every/Each/ When – All these will follow the same rules.
Eg: If our main statement reads as:

The ground is wet if it rains.

We now need to identify the cause and effect in this sentence.
The cause is “It rains”.
The Effect is “The ground is wet”.
This is an If statement.
Based on this let us now understand how the effect affects the cause and vice-versa.

As we have discussed earlier only certainties should be taken into account while solving logic related questions.

Hence, we can summarise:

For an IF statement, Cause happens effect will happen. Effect did not happen cause will not happen.

• Only If/ Only When.
Main statement - I eat only if I am hungry.

Cause – I am hungry.
Effect – I eat.

Hence, we can summarise:

For an ONLY IF statement, Cause does not happen effect will not happen. Effect happens cause will happen.
• Either - Or/ Neither – Nor.
Main Statement: Either Sachin plays cricket or Rahul plays cricket.

In these kinds of statements, the negation of one and positive of another is the logical sequence. If we consider the positive sentence before the negative then it will become a possibility.
Therefore, the correct sequence will be:

Rahul does not play cricket, Sachin plays cricket.
Sachin does not play cricket, rahul plays cricket.

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