Please note that valid syllogisms are based on very tight logic, bound by strict rules. When the premises are true and the rules followed, then the conclusion must be valid. Solid syllogisms don't leave much room for argument. That leads us to enthymemes. Enthymemes are used when the logic isn't quite so tight, when what we have to go on are probabilities and signs .
Probabilities express a premise, imply a second premise, and express a conclusion.
Probability enthymemes are slippery little devils. When you spot one, look closely at the logic, both expressed and implied. If you can convert the enthymeme into a valid syllogism, ok. Chances are, however, that sloppy logic was used to write it in an attempt to provide a text with a veneer of logical appeal. Signs are slightly more reliable enthymemes.