A syllogism is a type of logical reasoning where the conclusion is gotten from two linked premises. Here’s an example: An apple is a fruit. All fruit is good. Therefore apples are good.
Used properly, syllogism can be a good way of reasoning, but it’s very easy to make sloppy syllogisms by messing up the middle term that links the premises together, as in: "President Franklin Delano Roosevelt was an Aquarius. President Franklin Delano Roosevelt was great. Therefore all Aquariuses are great." Because so many are made poorly, the syllogism has a bad reputation. Poor, misleading, or tricky reasoning is often called “mere syllogism.”