A syllogism, probably developed by Aristotle, is where a conclusion is inferred from two  premises, one major and one minor, that each have one term in common with the conclusion. For example:

• Major Premise : Chris rolls over when he is happy.
• Minor Premise :  Chris rolls over when he is outside.
• Conclusion: Chris is happy when he is outside.

If I were to reverse the order of the premises, that would mean that if Chris is happy, he is outside. That’s almost true but he is also happy when he is on my desk making it difficult to finish a blog post.