a fortiori is a Latin phrase that means, having successfully argued for the stronger argument X, you can reasonably conclude the weaker argument Y.
Some examples:
It’s been established here that John is a medical doctor, a fortiori, he’s attended college and is familiar with the concept of a syllabus.
You’ve previously agreed with me that hunting animals for sport is morally wrong, so I can’t understand, a fortiori, why you think fox hunting is not OK.
a fortiori literally means from the stronger. The more complete version is, argumentum a fortiori.
(Source: Wikipedia)
