The blognet is full of people posting their own opinions, and that's a good thing. What is a little less supportable is flawed argumentation.
I recently spent some time discussion a post about software engineering; I was trying to figure out why the author thought what he did. The annoying bit was that his arguments boiled down to "I'm right because I say I am, and you can't disagree because it's a matter of logic: I'm starting from the axiom that A is true, and since my conclusion (A is true!) follows from that axiom, there is no argument possible." That is true as long as you acknowledge his starting axiom, but of course interesting discussions don't ever follow from this style of argument.
I see three categories of argumentation.
First, math-logic, in which the axioms and ground truths are given, and the rules of logic are applied to reach some conclusion. Conclusions are interesting only when a non-trivial result is reached: Euclidian Geometry is an excellent example, where 5 postulates lead to a plethora of interesting results. The drawback is that math-logic is very rarely directly applicable to reality: why (for example) Hilbert spaces apply directly to physical processes, and how far we can take this kind of correspondence between formal math and messy physics, is a fascinating and open topic of discussion.
The second type of argument is scientific, in which falsifiable statements are made about the real world. The distinction here is that a scientific theory must make predictions, and if those predictions are found to be false, then the theory itself must be false as it stands. Again, conclusions here are only interesting when the predictions are non-trivial with respect to the starting point: Quantum Mechanics and the Standard Model are both good examples, because (even though they must be wrong in certain regimes) they both make a large number of testable predictions. Evolution is a bit more controversial, scientifically speaking, because the predictions it makes have more wiggle room: however, specific predictions about how protein sequences should behave have been made and verified.
Third, rhetorical (using rhetoric in the sense of "verbal communication; discourse"). In rhetorical arguments, people start from positions that may or may not be well defined, but in any case are open to disagreement; participants are seeking to convince other participants as well to explore their own arguments. When Paul Graham writes about how Essays help him reach "surprises", he is talking about the most interesting kind of rhetorical argument: one that helps you realize truths that flow naturally from your internal precepts, modified by opinions and facts from the real world.
Rhetorical arguments are by far the most common on the Internet, and people often try to masquerade them as math-logic or scientific arguments. This is because math-logic and scientific arguments are both much stronger kinds of arguments; they lead to some notion of "truth", in either logic-space or reality-space. By contrast, rhetorical arguments are much less well-defined in both their starting and ending points, and (when two stubborn people conduct them) usually end in one or both people simply leaving the discussion. This is especially true when either of the participants refuses to discuss the precepts leading to the discussion: after all, if you're not starting from the same assumed ground truth, then the discussion can only rarely conclude with agreement; the main point of the discussion should then become to figure out where you differ in your assumptions.
Getting back to the frustrating blog post interaction that led to my post, then, the author started by asserting a moderately strong statement, and then defended himself against all comers by stating that "it was simply a matter of logic". This was undoubtedly true: asserting fact A and then concluding fact A is, in fact, a matter of logic. However, it is not interesting.
After probing a bit, I figured out that:
- the author's argument, stripped of language, really did boil down to an assertion followed by a conclusion based immediately on that assertion.
- the author explicitly rejected the notion that their conclusion could be falsified in any way.
Thus the argument was not an interesting math-logic argument (because the conclusions followed immediately from the precepts) and it was not a scientific argument (because the conclusions were not falsifiable). The only potentially interesting part of the argument was rhetorical -- and the author also explicitly rejected discussion of his initial axiom, rendering that uninteresting.
I probably wouldn't have gotten irritated, either, if the author hadn't decided that my comments, still polite and on-topic, weren't worth posting any more. Since they continued posting the sycophantic "what a good idea! <gush>" comments, I concluded that the whole point of the post was simply to garner attention. Disappointing ;(.
Math-logic: when interesting conclusions follow immediately from assumptions, that tells you that the assumptions contained that of interest; turns into a rhetorical argument about the assumptions.