Generally speaking, the best arguments also tend to be the more precise arguments. Precision in arguments is an important step in making them more coherent, more comprehensible, and free from flaws. Precision means that both the arguer and the listener are able to develop a better grasp of what the argument says and means. It follows, then, that vagueness in an enemy of sound arguments.
Vagueness is sometimes confused with ambiguity, a flaw in arguments which can be manifested as any number of different informal fallacies. Ambiguity, however, is the existence of multiple valid interpretations of words and ideas; vagueness is the absence of a clear and coherent meaning for the words and ideas being used.
Vagueness is also not something that inheres in words: what is vague in one context might be perfectly adequate in another situation entirely. For example, if you are filling out an insurance application it wouldn’t be appropriate to list your age as “over 21,” but if you are trying to purchase alcohol, that may be quite adequate to show that you are of legal age.
Vagueness generally occurs when an answer or argument fails to provide the information necessary to make a decision or reach a conclusion. Vague statements might also be offered as evidence for empirical claims when evidence is requested. Vague evidence is no real evidence at all, however: the vagueness prevents anyone from seriously evaluating and considering the information offered. Evidence for a particular claim must be particular to that claim and it must be show that it isn’t evidence for some other claim — vagueness is just the opposite of that.
Vagueness prevents effective communication because communication requires the exchange of information. This, of course, is the reason why vagueness is a flaw in someone’s reasoning or argument — if information is not properly communicated or conveyed, the entire purpose of the reasoning or debate process is undermined.
Why does vagueness occur in arguments? There are a number of possible reasons, some more excusable than others. In some cases, a person might be deliberately vague in order to avoid committing herself to any particular course of action - this is a feature of the arguments and statements made by politicians so often complained about by members of the public.
In other cases, a person might be deliberately vague in order to avoid admitting something unpleasant. For example, a person might realize that their arguments have been defeated but is not yet willing to acknowledge that fact. As a consequence, they might offer some vague statements meant to imply acceptance of the opposing side but never quite confirming it, leaving it an open question as to just how the discussion really ended after all.
It should not, however, be assumed that vagueness is always deliberate. Sometimes, and perhaps most of the time, it occurs because the person constructing the argument simply isn't doing a very good job at explaining their position. It may be that they don’t comprehend the issues as well as they think, and as a consequence aren't able to present their ideas in a precise and clear manner. This is not uncommon when dealing with someone who has very strong beliefs but is wholly unaccustomed to having those beliefs challenged and questioned.
If we want our arguments to be sound and for others to give those arguments due consideration, we must strive to be as precise as we can — at least when relevant. We should certainly refrain from being deliberately vague, but we must also make an effort not to be accidentally vague. When we see vague arguments from others, we should ask them to offer more precision and be prepared to explain why precision on that particular point is necessary.
