Ordinary-Language Example #1: You must have left your jacket in the car, dear. You were wearing it last night when we left the house. Since then, you’ve mostly just been in your room, and it is not there.
Can we find some structure of support here—one claim being supported by one or more of the others? Isn’t it the first claim in the example that is meant to be informative? The example itself suggests that we should imagine someone looking for their jacket, not quite sure where it is. So, again, that first claim is meant to fill in a gap in knowledge, making it “contentious.” The other claims do indeed seem to support the first.
To rephrase: We know your jacket made it to the car with you last night, and we know that you have spent almost all your time in your room since you came into the house from the car. This suggests that your jacket is either in the car, or in your room, but we (seem to) know it is not in your room (the example invites us to imagine that an exhaustive search has already been executed). Thus, it is highly plausible (at least) that your jacket never left the car when you exited the car to return to the house last night. Therefore, it remains in the car. Our example satisfies the definition we’ve provided of “argument,” and the commentary accompanying the definition has helped us to understand how this argument is supposed to work.
Ordinary Language Example #2: Why does light roast coffee typically have a higher caffeine content than dark roast? This is because caffeine tends to decompose during the roasting process, and dark roast coffee comes from coffee beans that have been roasted longer than the beans from which light roast coffee is made.
Is this second example a string of propositions, some of which support another?
The claims are clearly related, such that
“Caffeine tends to decompose during the roasting process”
“Dark roast coffee comes from coffee beans that have been roasted longer than the beans from which light roast coffee is made”
could logically support
“Light roast coffee typically has a higher caffeine content than dark roast.”
But the intention of the author does not seem to be to support (c). Rather, the claim made at the beginning of the string seems to be taken for granted; it does not seem to be controversial in this conversational context, and thus does not stand in need of support. Rather, the speaker seems to want to explain the first point with the points that follow. This is not what is meant by “support” in our definition of “argument.” To support a claim is to offer reasons to accept it when it is not yet taken for granted by one’s community, or, more narrowly, by one’s interlocutor.
As we have noted, less controversial claims should be offered in favor of more controversial ones.
(as already mentioned) the first claim in the string seems to be taken for granted as an interesting talking point in this conversational context;
It is difficult to see how what look like the “supporting” claims here would be less controversial than the supported claim.
Instead, all of these claims seem somewhat obscure or technical, apparently the sort of thing a coffee afficionado would know, while the rest of us would not. This string of claims does not clearly support the more obscure with the less obscure, or the less widely known with the more widely known. It appears that all the claims in the string are meant to be taken on faith, the speaker counting on his/her own credibility to back what is being stated here. With all this in mind, it appears that example #2 is really an explanation, rather than an argument.
As we can see here, explanations and arguments can have very similar structures, but the point of an argument is to persuade the interlocutor to accept a certain claim by offering support for it, while the point of an explanation is to help the interlocutor to understand why or how a certain claim holds true. An explanation thus assumes the truth of the main claim at issue, the claim to be explained, instead of offering reasons to some interlocutor(s) to believe it.