A syllogism is a kind of logical argument in which one proposition is inferred from two or more others (the premises) of a specific form. A syllogism has three parts: major premise, minor premise, and conclusion. The major premise of a syllogism makes a general statement that the writer believes to be true. The minor premise presents a specific example of the belief that is stated in the major premise. If the reasoning is sound, the conclusion should follow from the two premises. For example, if you know all squares are rectangles and all rectangles are shapes, and you deduce from this that all squares are shapes; this is an example of syllogism.
In order for a syllogism to be valid, at least one of the two premises must be affirmative. If both premises are negative, then no valid conclusion can follow. If both premises are negative, the middle cannot establish any link between the major and minor terms. For example, "All dogs can fly. Fido is a dog. Fido can fly." This is a perfectly valid argument in terms of logic, but this flawless logic is based on an untrue premise.