Continuing my series on tips for skeptics talking to faithful people, once you have a sense for why you are in the conversation, and why your counterpart is in the conversation, it's very useful to take stock of your intelocutor.
Here, we need to distinguish between a written exchange and an oral exchange -- and different kinds of oral exchanges. (Get your minds out of the gutter, I'm trying to be serious here.) When you're talking to someone face-to-face, that gives you the best ability to size them up. When you're talking over the phone, you lose some of the visual cues, body language, and other signals that tell you what is going on in your conversational partner's head. Even if all you've got is a written exchange, there are still subtle clues to look for.
First, you will want to make an assessment of your interlocutor's intelligence. Let me caution you that the risks of underestimating someone's intelligence far outweigh the risks of overestimating them. As a relatively new attorney, I once made the mistake of thinking that opposing counsel did not know what he was doing and falling victim to the prejudice that just because the guy had an aw-shucks attitude and used simple words and spoke with a vaguely Southeastern American accent, that he was kind of dim. Then he socked it to me with a brilliant legal argument and I walked away from the case with nothing but an unhappy client. Never again, I said, will I judge a book by its cover. Give your interlocutor the benefit of the doubt as to intelligence unless you are quite sure that you really are talking to a dummy.
Unfortunately, for better or worse we all do exactly this even after we've been burned the way I describe. Compare two men. Roughly the same height, same hairstyle, same posture, same race. One of them is wearing a suit, the other is wearing a T-shirt and jeans. You are likely to, at least subconsciously, assume that the suit-wearer is smarter than the T-shirt wearer. This is obviously not necessarily the case.
Another point I cannot stress enough is that the fact that your interlocutor disagrees with you is no indication whatsoever about her intelligence. This applies with particular force to skeptics talking to believers. There are lots and lots of very smart people who have religious faith out there, and you should not assume, even for a milisecond, that because you are the skeptic and the guy you're talking to is religious that the guy you're talking to is a dim bulb who is just parroting things his pastor has said without even understand what he's saying. Never never never think that without multiple and direct instances of proof to that effect. If you have to, tell yourself that smart people can have "blind spots" in their thinking, but more to the point, remember that a person's religious experiences are based on irrational factors like emotions. Smart and not-smart people all have emotions, emotional experiences, and psychological stressors that molded their personalities and preferences. You do too. You can be very smart and still be under the influence of these irrational and uncontrollable mental factors. And it's healthy to maintain the intellectual humility to admit that there's always the possibility that you are wrong.
As a general rule, the clues you will use to assess your counterpart's intelligence ought to be the extent of her vocabulary, her poise and confidence (frequently expressed in body language and eye contact), the logical consistency and structure of her arguments, her ability to relate relevant evidence to support her claims, and the degree to which she evidences understanding of the things you say to her. Also as a general rule, you should prefer a smarter conversational counterpart to a less smart one. Whatever your purposes to the converation are, a smarter partner will get you there in an easier, faster, and more satisfying way.
On the other hand, if despite a cautious assessment, during the conversation you find yourself continually drawn towards the idea that maybe the person you're talking to isn't the sharpest tool in the shed, then you need to start molding your arguments accordingly. Particualrly if you are speaking in a forum where you must appeal not only to your interlocutor but also to third parties, you should use simpler, plainer langauge. Eschew adverbs. Shorten your sentences. By all means, don't stop the discussion should you get the impression that you are not speaking to an intellectual equal; instead, make it a point to express yourself in a way that your target audience can easily understand you should it wish to do so.
And for crying out loud, don't ever say out loud to someone that you are assessing her intelligence or worse yet, what that assessment is unless it's "You're really, really smart." I can't imagine a more effective way to insult someone. Even if you want to sincerely compliment her intelligence, make sure you do it in an offhand way because in an argument, your interlocutor will frequently respond to a compliment by putting up her defenses, fearing that the compliment is a set-up to a sucker-punch.
Second, how one presents oneself matters. Consider my example above about two men who are roughy identical in appearance, one wearing a business suit and the other dressed casually. What we can say is that the suit-wearer has taken the time and trouble to put on formal clothing. This was an intentional act. Maybe it was done out of a sense of oblgiation, as in the case of someone who wears a suit because he has to. But even so, the suit is mandatory because someone wants this person to appear to be authoritative, to appear to be trustworthy, to appear to be respectable.
Context matters when considering your counterpart's dress and demeanor. If this is a beer-fueled bull session in a collegiate pub, you're going to view a suit and tie as out of the ordinary. If you find yourself in such a setting wearing such clothing, it can help to do something to your appearance to indicate that you've adopted a more relaxed attitude after being at a more formal event previously -- gents, loosen the tie and unbutton the collar; ladies; maybe you should literally let your hair down. Maybe even slouch a little bit in the chair. The point is to engage your conversational partner appropriately in context.
Now, if you're going to be in a formal debate, in front of an audience, it makes sense to go the other direction. Take the time to put on a suit, or at least more formal-than-usual clothing, to indicate that you are taking the proceedings seriously, and to assume an aura of gravity and intelligence. Ultimately, yes, you will be judged by what you say and not how you dress -- but the same statement delivered from someone wearing a suit gains credibility faster. And if you stumble, you will lose less credibility than you would if you look like a slob. If your adversary in a debate shows up dressed inappropriately, you will be in a better position to make attacks on his credibility.
Third, you must always understand the emotional stakes for your conversation partner. I'm aiming this advice specifically at skeptics talking to believers. Remember that for a lot of believers, the stakes in a conversation about their belief systems could not possibly be higher. For them, nothing less than the eternal fate of immortal souls are at issue -- something that, within the context of their world views, is more important even than life and death.
Don't assume that because you think there is no such thing as a soul or heaven or hell that your conversation partner is going to feel the same way. If you find their efforts at converting you annoying, at least understand that they in their minds, they are trying to save you from a terrible fate. It might seem ludicrously improbable to you that a meteor is about to crash down on your house at ultrasonic velocities and kill you. You would be right to be annoyed at someone running in to your house urging you to get out right now. But if that person sincerely and truly believed that the meteor was coming, doesn't that person have a moral imperative to warn you, to try and save your life? These are the emotional stakes for the theists who engage you in conversations attempting to convert you to their world views.
Similarly, when you advance a skeptical, non-theistic world view, you need to understand that your interlocutor has very likely tied up a great deal of her own identity, her own ego, her own way of looking at the world, in the very theism that you are calling in to question. So what to you may seem like an interesting and amusing discussion of an academic or philosophic issue, to your counterpart it may reach to the very core of their psychological being. When presented with claims like "There is no God," "There is no evidence that Jesus ever existed," or "The Bible is not a very good guide for moral conduct," you are shaking the very foundations of their existence. They will take these things personally because so much of their personality has melded with the concepts that you are rhetorically demolishing. I'm not saying don't make those contentions -- I'm saying that you need to find some way to cushion their landing.
Example: "Christians are generally very good people morally, but the reason for that is not the Bible but rather their innate desire to be morally good. Christians are good despite, and not because of, the teachings of the Bible." Now, you've assured your interlocutor that you aren't making a personal attack, that you do not dispute that he and people like him are good people, and you've framed the issue in such a way that Christian doctrine, and not Christians as individual people, are what you are discussing. To the devoted Christian, especially one who has never before even considered the possibility that the Bible might have parts in it that are bad, this is a disturbing enough image. That's why you need to go out of your way to not allow your interlocutor to even guess at the possibility of your remarks being a personal attack.
Now, you might have an interlocutor who has a strong enough psyche to not perceive your existence or your arguments as existential threats. Which is good, and healthier than what I've just described. Nevertheless, such a person may still feel that their interests in demonstrating the validity of a particular religious belief are vested somehow.
A person with heightened emotions about the subject matter of your discussion is going to present you with a greater likelihood of saying something really silly when his emotions get the better of him, but at the same time you run the risk of getting into a situation where fallacies are endorsed and volume and invective are enlisted to supplement evidence and argument. Emotions are the enemy of rationality and you will generally want to defuse your interlocutor's emotions whenever possible -- unless your tactic is to drive your interloctuor into an emotional frenzy as a means of displaying their irrationality.
With these three things in mind, you will be able to assess the quality of your conversational counterpart, and thus anticipate the kinds of tactics and rhetorical devices that your interlocutor will employ to advance her objective. You will be able to devise responses that better advance your own agenda. Also, you will be able to tailor your own statements so that they achieve maximum impact.