What counts as having common ground?

"Common ground" happens to be one common phrase that Gangadeanians use. It certainly isn't Gangadean's concoction. It's a pretty common saying among philosophers. But the way it is used by Gangadeanians (as the basis of excluding or including people in conversations) makes me think they have a rather different notion than that of most of the philosophers ("on the outside") that I have encountered.

Gangadean often asks whether there is any common ground between his interlocutors and himself. Only if there is, will there be "room for discussion." Without "having" common ground he claims that further discussion is pointless. As with pretty much anything in philosophy, all of this might appear at first glance as a rather straightforward idea. You might be thinking, what is so tricky or unclear about "the need for common ground in advancing discussions? If we don't have enough in common, then we won't get anywhere in talking about things." But it turns out this is anything but simple and straightforward. When Gangadean asks whether there is sufficient agreement, or whether he and his conversation partners have common ground, we need to ask what it means in the relevant sense to agree on claims or what it means to have certain claims in common.

There seems to be a sense of having "common ground" as it pertains to a particular conversation. Say that you go into an ethics seminar and you pronounce that there is no point in discussing ethics and you stick with this sort of disposition. Your assertion and the sorts of objections you will raise (if you follow your disposition through and through) will no doubt prove disruptive. You have a meta ethical view that denies one of the unspoken presuppositions of the ethics class--people engaged in an ethical discussion have it as common ground (in some suitable sense) that ethics is within the realm of things worth studying.

But the crucial issue is how we should characterize the sort of propositional attitude** that two people must be in with respect to a proposition or set of propositions, in order for them to count as "having" the proposition(s) as common ground.For instance, do each of the speakers have to believe that ethics is a worthwhile field of study for that claim to count as common ground between them? If they have any doubts about the matter, at any time, does it no longer count as common ground and thus render talk about ethics pointless?

Or do they have to know (rather than merely believe) that ethical inquiry is worth pursuing in order for it to be part of the common ground between them?

Or do we require that they have to know with certainty (as Gangadeanians seem to)?

Of course there are many many gradations to take note of given the complexity of mental states like belief, doubt and the like. Some believers are just more confident in their beliefs than others. Provided that you accept that beliefs come in degrees, we would also need to consider all the different varieties of belief and again ask whether believing to each degree in the common ground proposition, counts as "having" common ground. Or we could speak of beliefs as it pertains to the various levels of support they have via the subject's evidence (which could get us a number of gradations as well). We should also consider cases of doubting and its various degrees. A person might have slight to serious doubts about whether ethics is a worthwhile study, but desire to dialogue about ethical theories in an effort to see where it might lead. They might even come convinced by seeing the fruits, that ethical inquiry is a worthy task even if they weren't at the outset. My point is, it isn't clear which of these attitudes (doubting, believing, knowing, knowing with certainty) two persons must be in with respect to some proposition(s) for it to count as a case of having that proposition(s) as common ground.

In my experience, Gangadeanians seem to think it is knowledge with certainty, which is the most stringent of the one's we've considered. This state is such that once you "accept" a proposition, you cannot intelligible call it into question, ever again. The laws of thought, basic distinctions (as Gangadean defines them), causation, that reason is ontological, and the like must be known with certainty and never doubted gain by those involved in talking with a Gangadeanian for discussions to be meaningful. My last encounter with Gangadean, in his office was basically him asking me if I agreed to certain "truths." When I said that I believed many of them, but didn't take myself to be certain of them, he found this unacceptable and grounds for ending discussion.  [The sharp reader will consider why the Gangadeanians stop at epistemic certainty. Might not there be an more stringent of common ground like diachronic certainty--such that in order to count has having common ground, two persons must know propositions with epistemic certainty and immutability. In other words, why stop where the Ganagadeanians have chosen to draw the line?]

But this not only seems entirely wrong, it is also unsupported. Again, just why should we accept where Gangadean has drawn the line (why not think that common ground regrading some proposition consists in merely acknowledging for the purpose of the discussion at hand, that the common ground propositions are assumed to be true)? Again, they have drawn a line, but it seems arbitrary. To be clear it seems like the Gangadeanians believe that common ground is necessary for worthwhile discussions. But to have common ground in some proposition or set of propositions requires that each side knows the proposition(s) in question with absolute certainty. Thus worthwhile discussion is only possible if the members of a given discussion each know with absolute certainty the common ground propositions.

Let me try to explain why I think this is a bad view. Philosophers often entertain the views or presuppositions of others in order to try and show that a view is not internally inconsistent. This is a really common practice in professional philosophy. To be sure, this doesn't mean that they actually believe, (let alone know or know with certainty) the presuppositions of their interlocutors. They just assume them for the purposes of discussion in order to show how under those very assumptions, problems arise.In the same vein, consider reductio ad absurdum arguments or proofs by contradiction. You certainly don't buy into the premises of such argument types. Instead you set out to draw out a contradiction that follows from accepting the premise(s). Sometimes you might simply be on the fence about whether a premise is true and you try to derive a contradiction which will show you that it is not true. Other times, you suspect or even know that the premise can't be right, and you just want to show someone else explicitly how it leads to a contradiction.

So these are cases that I take to be fruitful dialogues. After all, they point out inconsistencies or contradictions that may follow logically from taking certain things for granted. And there is a very weak sense in which there is common ground. The persons involved in such dialogues at least assume (for the purposes of discussion) certain claims, including the premises that one person hopes to show leads to contradictions. But none of this requires anything like knowing the common ground propositions with absolute certainty.

So why should we think Gangadean is right in thinking that in order for two or more persons to have a fruitful dialogue, the participants must all know with absolute certainty certain propositions (i.e,. common ground propositions)?


**Note a propositional attitude is often thought of as a mental state which has as its content, a proposition. You might believe that the sun is warm, just like you might remember that the sun is warm, or see that the sun is warm, or desire that the sun be warm, or even know that the sun is warm. Each of these sentences expresses the idea that you are in a kind of mental state which has a proposition as its object--the thing expressed by the clause following 'that' in each instance. That's what I roughly mean by a propositional attitude.