Another core characteristic of Rational Painting is our insistence on rational discourse and critical thinking. The art world is plagued by emotionally-charged language and disputes that can become bitter and heated, and we are not interested in that here. We expect all of our members to be civil, and to seek the truth through careful and rational discourse rather than the "brute force" of argumentative tactics.
Reduced to a simple statement: you can say anything you like on Rational Painting as long as you are prepared to defend it in terms of reason. However, this is much more difficult than it may seem. We want people to think clearly, disregard dogma, and recognize their own biases, and realize that this is not easy. Guides to logical and rational thinking can be great helps in this area, as they can help you to recognize flaws and fallacies in your own thinking, as well as other people's, and that is essential for finding truth.
The following is a small sample of the sorts of arguments that frequently pop up on art forums, and which we do not tolerate here. It is not an exhaustive list; please see the "Recommended Reading" section at the end of this article for some sources for further study.
False Dilemma: Presenting two options to choose between that are not mutually exclusive. For example: "It is better to be expressive than to be accurate in painting." This is a false dilemma because it is possible to be both expressive and accurate in painting. There is no need for a choice between the two.
Slippery Slope fallacy: the implication that a step in a given direction will result in continuous motion in that direction until a (usually disastrous) end. For example: "Using photography in painting leads to tracing and the elimination of skill from art." This is a slippery slope because no evidence is given that this progression will take place, and it posits emotionally-charged consequences for a series of events that will not necessarily occur.
Arguing from Authority: unsubstantiated statements that seek credence based on the speaker's authority or expertise rather than empirical evidence. For example: "A painter should not measure; I've been painting for (x) years and have never measured." This is an argument from authority because the speaker offers no evidence for the truth of his assertion, and substitutes a statement emphasizing his experience. It does not establish the truth of the statement.
Red Herring: a diversionary tactic used to attract attention away from a previous statement, or argue a different point. For example: "We don't need to use Munsell. The Old Masters didn't use color systems." The claim about the Old Masters is irrelevant (not to mention vague and unsubstantiated), and it doesn't substantiate the first sentence.
Straw Man: misrepresenting an opponent's argument in a way that bears some outward similarity, but which alters it fundamentally so that it may be easily dismissed, without actually engaging the original point. For example: "(Person X) says that we have to know anatomy to be able to paint the figure well. If artists turn into walking textbooks, all of their work will be boring." No such argument has been presented, and the implication thereof is clearly absurd. The original argument has not been refuted.
There are many, many more types of irrational arguments that one may frequently encounter, but they all share the characteristic of a deliberate (if sometimes unconscious) attempt to use emotionally persuasive language to try to strengthen a weak argument. We do not expect all Rational Painting members to take courses in logic, but we do expect everyone to work hard to avoid these and similar tactics in their reasoning.
These are a couple of inexpensive books on good thinking that we recommend, although of course this is a small sample. Again, please note that although the links below give a small referral credit to Rational Painting (at no cost to you if you purchase them), you can of course obtain them from any source if you prefer not to use these links.
Being Logical: A Guide to Good Thinking, by D. Q. McInerny
A Rulebook for Arguments (4th Edition), by Anthony Weston
Wikipedia also has a comprehensive list of fallacies that is worth a look.