IRAC. I do it every day. You figure out what the issue is, determine the most appropriate rule, apply the rule to the circumstances, and get your answer.
Common sense. I use it every day, too. You look at a situation, stick it into your intuition, and wait for the answer to pop out.
We call the steps in the process by different names, but you usually get the same results. IRAC just tells you why and how you got there. Common sense is like flying up to Minneapolis; IRAC is like taking I-35. You don't even have to know what you're doing when you use common sense, but if you don't know how to use IRAC or you don't use it right, you could end up in San Francisco after accidentally turning left in Des Moines.
I like to think about this kind of stuff. How the brain and/or mind works. Maybe that's why this article, comparing psychology and common sense, was so interesting to me. Here's my favorite quote:
Ultimately what really sets psychology apart from common sense is the scientific method.
once psychological findings become well-known, people [might] incorporate them into their intuitive thoughts and behaviour.
And then it becomes "common sense."