The former are defects in structure, errors in the pattern of the argument that render it invalid, usually independent of the argument’s specific content.
The latter are often breaches of procedure rather than structure, attempts to thwart the goal of a critical discussion, often to merely ‘win’ the argument than to achieve better understanding, to obscure truth rather than reach it. Many informal fallacies are not always fallacious.
Fallacy theory is a complex subject, and not all logicians agree on the definitions I’ve just given, but that’s cool. Fallacies can be used to distract and mislead, or they can be used in reverse, in labeling argumentative strategies, to reduce their effectiveness by calling attention to them when abused.
In some debates, such labeling will be done fairly frequently, in others, more subtle counterstrategies will be used rather than explicitly pointing out the fallacies. In this case, knowing thine enemy and naming it is useful, subjecting the flawed argument to scrutiny, and lessening its sting.
But that is not enough. And it pays to not be a dick when debating.
To argue that naming a fallacy shows the claim of an argument false is to commit the fallacists’ fallacy, as it it entirely possible for an argument may be weak, its claims not following from the premises, but the claim made can still be correct despite the argument made for it.
It is also committing the fallacist’s fallacy to falsely accuse one’s opponent of arguing fallaciously, when a fair evaluation of their argument and its context would clearly show the argument valid. Context matters with argumentation!
So it is not enough merely to label an argument. In fact, it’s advised that you don’t, at least not in an arrogant manner. What’s needed is to use your knowledge of how the argument goes wrong to craft an even better counterargument, assuming that it’s even important enough to refute. Not all arguments are, as some may be simply ignored if not worth the time spent ‘attacking’ them.
There’s a military metaphor in that, an unfortunate artifact of the history of argumentation that has given the entire field of study a reputation for quarrelsomeness and bickering.
That’s especially the case with logical inconsistencies and outright contradictions. If two or more arguments work at cross-purposes, logically at least one of them must be rejected, but the natural human inclination is to throw them all out, as reflecting poorly on the arguer’s credibility and even resulting in loss of the argument.
Even fallacious arguments sometimes assert things that are true, being right for the wrong reasons, but they cannot reliably show those things to be the case. Logic alone proves nothing, even if the argument is formally or informally valid or uses strong inference.
For that, we need objective data as well.
We need the best evidence available to support our premises, which must not only be true, but which must also be acceptable, clear, relevant, as non-circular as possible, and as free from unwarranted assumptions and presumptions as can be had.
Tf. Tk. Tts.