One precondition for genuine and fruitful ecumenical dialogue is understanding the difference between sophistry and rational dialogue, and being sufficiently self-disciplined to engage only in rational dialogue and avoid all sophistry. Rational dialogue is a mutually shared act aimed at the discovery and acquisition of truth. Sophistry, on the other hand, is not a mutually shared act, and it is not aimed at the discovery or acquisition of truth. Sophistry makes persuasion the highest goal of one's communicative activity. Implicit in that goal is the preservation of one's own position, hence a sophist is also an ideologue. True ecumenical dialogue must be rational dialogue, not sophistry. (To see the difference between rational dialogue and sophistry, I recommend Plato's Gorgias, which I have my students read whenever I teach ethics.)
Three signs of sophistry:
First, the ad hominem. If the subject of the proposition is the interlocutor, and the predicate of the proposition is critical, then, strictly speaking, the proposition is an ad hominem. An ad hominem is any criticism of one's interlocutor, instead of (or in addition to) criticism of his claims, positions or arguments. Critical statements beginning with the word "You" (in the context of a conversation) are almost always ad hominems. So are statements that begin with "You are not ... ", or "You forget ....", etc. So are most statements that begin with "You want ...". The interlocutor's claim or argument is there 'reduced' to the interlocutor's desire, and criticized as such. Ad hominems are fallacies because they direct attention away from the truth or falsity of the claims or positions advanced by the interlocutor, or the soundness/unsoundness of the arguments advanced by the interlocutor, and instead direct attention at the interlocutor himself. Well-trained interlocutors in a rational dialogue aimed at the discovery and acquisition of truth have developed the habit of avoiding all criticisms of the interlocutor; they have by discipline and practice learned to focus their criticisms only on the claims, arguments or positions in question. Sophists or ideologues, on the other hand, do not hesitate to criticize the interlocutor, because their goal is not the mutual pursuit of truth, but persuasion, both of the interlocutor and especially of the observers of what in their minds is the spectacle of a "debate" or "contest". And sophists know that the observers [who are not trained to distinguish sophistry from rational dialogue] can often be persuaded by means of techniques that involve attacking the intelligence, character, education, sincerity or credibility of the "opponent", and thus creating the appearance that the other person's claims or positions are inferior, and that one's own position is superior. So one way to determine whether one's interlocutor is engaging in sophistry or is pursuing a rational dialogue is to see if he or she is making use of ad hominems. When one of the interlocutors resorts to ad hominems, this is an indication that his goal is not truth, but 'victory'.
Another sign that an interlocutor is not engaged in rational dialogue is that he evaluates claims by some criterion other than truth. For example, it is not uncommon to see claims or positions rejected as "old" or "tired" or "worn-out" or "tiresome". The proper evaluation of an argument has to do with its soundness. Are its premises true? Does the conclusion follow logically from the premises? Similarly, the proper evaluation of a claim is whether it is true. The age or familiarity of an argument or claim is irrelevant to its soundness. Whether the argument or position or claim is bothersome or irritating or annoying or familiar to the interlocutor are all irrelevant to the soundness of the argument or the truth of the claim or position. C.S. Lewis called this replacement of the quest for truth with the quest for novelty "chronological snobbery". Jacques Maritain called it "epistemological time-worship". It subordinates truth to novelty, and for that reason it is a form of sophistry.
Another sign that an interlocutor is not engaged in rational dialogue, but in sophistry (or the preservation of an ideology) is rage, especially rage directed toward the interlocutor, even if the speech is directed to the observers. (This is why rage can take the form of a rant.) We can see rage of this sort in the character of Thrasymachus, in Plato's Republic. The truth-seeker (and truth-lover) has no reason to be enraged at his interlocutor, or engage in a rant about him. If the claims or positions or arguments offered by his interlocutor are false or unsound, then he simply has to show them to be such; there is no reason for him to be angry with his interlocutor. If, on the other hand, the claims or positions or arguments offered by his interlocutor turn out (upon critical evaluation) to be true, he is prepared to accept them, since he is, after all, a truth-seeker. Either way, he has no reason to be angry when his interlocutor presents claims or positions that differ from his own. The ideologue, on the other hand, seeks ultimately to preserve and advance his own position. Hence, the ideologue grows angry when his interlocutor advances positions or claims or arguments that are contrary to his own (and praises and embraces all who support and defend his own position, even if their arguments are fallacious or their praises mere flattery). He is not prepared to accept a position other than his own, and hence criticisms of his position are perceived as threatening, and that is why he responds to them with hostility, just as animals often respond with hostility when they perceive something as threatening. Anger and rage in a discussion are a sign that defending an ideology has taken the place of seeking truth as the goal of the activity. Indifference is sometimes even a greater sign of ideology than is rage. The ideologue of this magnitude no longer even cares if there is evidence or argumentation that refutes his position; he has made his ideological bed and he is going to sleep in it no matter what, so he is utterly indifferent to criticisms of his position.
In order to have fruitful ecumenical dialogue, the interlocutors at the ecumenical table must all be the sort of persons who not only understand the distinction between rational dialogue and sophistry, but have disciplined themselves by training only to engage in the former, and to avoid the latter. To love Christ is to love Truth. And hence rational dialogue is an activity aimed ultimately at Christ; sophistry aims at something less.
"Let unity, the greatest good of all goods, be your preoccupation." - St. Ignatius of Antioch (Letter to St. Polycarp)