Syllogism based questions in Verbal Reasoning

There are two branches of logic – Deductive and inductive. Deductive logic is the process of reasoning from one or more than one premises to reach a logically certain conclusion. In Deductive Logic you begin with the premises that are assumed to be true. You then determine what else can be true if the premises are true.

 Syllogism (Pronounced as See-lo-jism) is a part of deductive logic. Syllogisms are basically questions that can be solved using Venn diagrams. These questions do not appear in CAT, but appear in all the other exams like SNAP, XAT, CMAT etc. Although they do not appear directly in CAT, but they help in enhancing one’s reasoning skills and are thus useful for identifying the arguments and premise.

In Logic, a statement which is logically correct and is not open to questions is treated as a Certainty. A certainty will not change by introduction of additional data. On the other hand, a statement which is open to question and can be altered by the introduction of additional data is a Possibility. Syllogisms can be solved using the concepts of Some, All, None and Only. Let us look what they mean:

• Main Statement: Some A is B / Some A’s are B’s

Based on the above Venn diagram lets list down the certainties i.e. all the scenarios that will surely be true:

• Some B’s are A’s

Possibilities i.e. the scenarios that could be true in some cases:

• All A’s are B’s
• All B’s are A’s
• A is B or B is A

Based on the above Venn diagram lets list down the certainties i.e. all the scenarios that will surely be true:

• Some B’s are A’s

Possibilities i.e. the scenarios that could be true in some cases:

• All A’s are B’s
• All B’s are A’s
• A is B or B is A

•  Main Statement: All A is B / All A’s are B’s

Following are the certainties:

• Some As are Bs
• Some B’s are A’s

Following are the possibilities

• A = B, B= A
• All B’s are A’s

Main Statement: No A is B

Since there are no intersections in this Venn diagram there is no scope of possibility/ certainty.

Main Statement: Only A is B

Draw the Venn diagram of “only A is B” or “Only A’s are B’s”. You will find that it is another way of saying “All B’s are A’s”. So Only is nothing but All reversed.

One needs to remember these concepts to solve syllogism questions.                                                                  

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