If a substance is water, then its boiling point at sea level is 100C.
The law of syllogism, also called reasoning by transitivity, is a valid argument form of deductive reasoning that follows a set pattern. It is similar to the transitive property of equality, which reads: if a = b and b = c then, a = c. ... If they are true, then statement 3 must be the valid conclusion.
In simpler terms, law of syllogism is used when you have two conditionals and the hypothesis of one matches the conclusion of the other.
Syllogism includes combining different quantificator with P and Q is possible to compose a table that deduces truth values depending from only the truth (or falsity) or the singular statement P and Q and from the structure (composition) of the syllogism, without even considering what are practically P and Q.