From Larry Solum's Legal Theory Lexicon: Vagueness and Ambiguity. From the introduction:
This week the Legal Theory Lexicon entry focuses on "ambiguity" and "vagueness"–two important concepts for the theory of interpretation. Some legal texts are ambiguous–they contain words or phrases that can have two or more distinct meanings. And some legal texts are vague–they use concepts that have indefinite application to particular cases. And some legal texts are both vague and ambiguous–they have multiple meanings, some (or all) of which have indefinite applications. Because "vagueness" and "ambiguity" are basic concepts in the theory of interpretation, its important to master each of them and to understand the difference between them.
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What does it mean to say that a concept, term, or phrase is vague? Let's start with some examples and then try for an elucidation of the concept. "Tall" is a good example of a vague concept. Some humans are definitely not tall–Danny DeVito, for example. Others definitely are tall–Boban Marjanović, for one. But the term "tall" is vague. 5'11 is almost definitely tall for a woman in the United Sates, but might be a borderline case for men. "Tall" is not the sort of quality for which there are definite criteria that sort the world into "tall" things and "not tall" things. In other words, "tall" is vague.
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What about "ambiguity"? A word or phrase is ambiguous if it has more than one meaning. Take "cool" for example. One meaning of "cool" has to do with temperature, and in this sense, "cool" contrasts with "warm," "cold," and "hot." Another meaning of "cool" has to do with fashion and social attractiveness. And there are other senses of "cool" as well, as in, he kept his cool in a very pressured situation. So, the word "cool" is ambiguous because it has multiple senses, with each sense representing a different concept.
And from later on:
Now that we have a basic grasp of vagueness and ambiguity, we are in a position to see that each of these two concepts has a role to play in a theory of the interpretation of legal texts.
Many legal texts are vague. In fact, most law students become very familiar with a variety of vague terms early in their law school careers. Take "reasonable"–was the tort defendant's conduct "reasonable" under the circumstances? There will be clear cases of unreasonable conduct: driving 150 mph in a residential area. But there will also be borderline cases. Was it reasonable to drive at 55 mph in a light fog?
Some legal language general, abstract, and vague. For example, the phrase "equal protection" in the 14th amendment of the United States Constitution might refer to a very general and abstract idea of equality. Given this generality and abstraction, it might be that the "borderline" cases seem to make up the whole of equal protection doctrine. What would count as a clear example of "equal" or of "unequal"? In a common law system, general and abstract language may be translated into relatively more particular and concrete rules through case-by-case adjudication.
Vagueness is ubiquitous in the law, and frequently legal actors (courts and others who apply the law) must resolve borderline cases. Every law student is familiar with the strategies that are employed, which include case-by-case balancing tests, supplementary doctrines that provide bright-line rules to implement vague legal texts, and so forth.
Ambiguity may be less common, because many potentially ambiguous terms or phrases are disambiguated by context. "Seizure" can refer to a physical taking or it can refer to a medical symptom, but in the Fourth Amendment of the United States Constitution, it is clear that the correct meaning is the former rather than the latter….
Posted at 6:02 AM