Tilly's chief insight is that reason-giving is social and relational: When people try to explain unusual events, they're not trying to get at the truth so much as they're trying to maintain their relationships with other people.
Tilly enumerates four ways we try to make sense of things: conventions (polite sayings), stories (dramatic personal narratives aimed at cause-and-effect reasoning), codes (legal and ritualistic formulas) and technical accounts (detailed scientific explanations).
An illustration: Suppose a guy named Darrell stores old car batteries next to his house. One of them explodes, and the acid seeps across his property line, contaminating his neighbor Joe's shrubs and nauseating Joe's cat.
"Just one of those things," mutters Darrell, not really attempting to explain anything but hoping to brush off the accident and maintain his relationship with Joe: That's a convention. "Well, it all started when I went to the discount auto parts store," Darrell tells his cousin, beginning a detailed narrative that tries to account in everyday terms for the accident's origin (a story). But Joe hires a lawyer, and soon there's talk of torts and liability -- in which the goal isn't ascertaining truth as much as it is observing legal precedents (a code). Finally, biohazard experts, faced with many such battery explosions, detail scientific origins and remedies for the accident that befell Darrell and Joe (a technical account).
The payoff of Tilly's four-part grid is that it helps articulate why we're disgruntled by so much inappropriate reason-giving. A polite convention isn't enough to offer a good friend going through a painful divorce; nerdy technical accounts won't comfort poor Joe with his sick cat. Moreover, we're not the tidy little truth-tellers we'd like to think: We're more interested in managing people than sticking to facts.
Ironically, in a book subtitled "What Happens When People Give Reasons ... and Why," Tilly doesn't explain himself very well. He's too fond of meandering examples that detract from his theories instead of illuminating them. He's a sociologist aiming for a popular style, but he writes with his elbows.
Now that readers have heard my little story, however, they won't need to plow through his book-length technical account. As for my condensing your book into understandable snippets, Professor Tilly, I guess it's just one of those things. I hope you're not going to sue me.