How to avoid ambiguity
Minnesota Revisor's Manual 2013 Edition


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Ambiguity: An Overview

English has a multitude of ways to be vague, or over-general, or ambiguous, or all three, although the differences are important.
Ambiguity exists when words can be interpreted in more than one way. For example, is a “light truck” light in weight or light in color? Vagueness exists when there is doubt about where a word's boundaries are. If a law applies to the blind, who exactly is blind? What degree of impairment counts? Over-generality exists when the term chosen covers more than it should. If a law applies to “communicable diseases,” is it really meant to cover the common cold? Legislatures sometimes choose to be vague or general and to let administrative agencies supply the specifics. They rarely choose to be ambiguous.
Ranges Of Numbers, Days, Dates, And AgesSome other small words that cause trouble are the words we use to specify ranges of numbers, ages, and dates: to, through, between, and from.

When specifying a set that begins at A and ends at B, the drafter should make clear whether the named end points are included.

For ranges of sections in bills, statutes, or rules, it is acceptable and traditional to use a form such as “sections 1 to 20” because the laws on statutory interpretation make clear what the range means. They specify that in ranges of sections, the form “sections x to x” includes the first and last numbers and all sections between them. See Minnesota Statutes, section 645.48.

However, in other instances, the solution is not so easy; to is not synonymous with through.

For ranges of days, the drafter should avoid the use of to altogether. The phrase “Monday through Friday” includes all of Friday, but the phrase “Monday to Friday” includes all of Thursday and is ambiguous as to whether Friday is included. To be certain that Friday is included, the drafter should say “Monday through Friday.” To exclude Friday, the drafter should write “Monday through Thursday.”
Don't say

From July 1, 2002, to. . .

After June 30, 2002, and before. .
Don't say

Between July 1, 2002, and. . .

After June 30, 2002, and before. . .
Don't say

To (or until or by) June 30, 2002. . .

Before July 1, 2002. . .
Don't say

between the ages of 17 and 45

years old or older and under 46
Don't say

who is more than 17 years old

who has passed his 17th birthday [or 17 years old or older]

unless you mean who is 18 years old or older
That and Which

A possible source of ambiguity is the word which used without commas. The general rule is that that should be used to introduce restrictive clauses (those that are necessary for meaning), and which, with commas, should be used to introduce nonrestrictive clauses (those not necessary for meaning). If a drafter uses which without commas, a reader may be unable to tell whether the clause is necessary for meaning. The drafter will need to decide whether to change which to that or add commas. Often the best solution is to redraft the sentence entirely.
For example, in the sentence—

A report which is required to be available for inspection must be in a form convenient for photocopying

—which of the following is meant?

1. A report, which is required to be available for inspection, must be in a form convenient for photocopying.

(In other words, all the reports have to be made available and all have to be in a certain form. This could be redrafted as The office must make the report available for inspection and must preserve it in a form convenient for photocopying.)

2. A report that is required to be available for inspection must be in a form convenient for photocopying.

(In other words, the reports that have to be made available are the only ones that have to be preserved in a certain form; others do not. This could be redrafted as If a report is required to be available for inspection, it must be in a form convenient for photocopying.)
Serial Commas and Ambiguity

The revisor's office uses a style that calls for a comma before the conjunction in a series. A drafter should think carefully, though, before adding a comma to a sentence written by someone else. In rare cases, such a sentence may be ambiguous.
Here is an example:

The commissioner shall assign to the case two managers, a program specialist and a family visitor.

How many people are being assigned to the case? Without a comma, the sentence can be read to mean two or four people. Make certain that the original drafter meant four people before adding the comma. (If the drafter meant two people, rewrite the sentence.)
Ambiguity At The Sentence Level

(a) The placement problem.

Often ambiguity is the result of unclear sentence structure or poor placement of phrases or clauses. For example, a sign about refunds at a local hardware store reads “Store credit only after 90 days.” Does this mean that after 90 days, the customer can receive a refund only in the form of store credit? Or is the point that store credit is not available as a form of refund until 90 days have elapsed? The placement of only makes the reader unsure.
Phrases that specify time also need to be placed carefully. Consider this example:

The public school district shall inform the nonpublic school of the type, level, and location of health services that are to be made available to the nonpublic school students before August 15.

Are services to be made available before August 15, or is the district to inform the school before August 15? Placing the words before August 15 at the head of the sentence or after inform the nonpublic school would make it clearer that the date is a deadline for supplying the information.
(b) Modifiers of nouns.

Combinations of nouns and their modifiers are often a cause of trouble. A modifier is a word or group of words that tells more about another word's meaning.
In the examples that follow, the modifiers are italicized.

the escaped prisoner
the executive officer of the county
an order that has been signed by the governor
an order signed by the governor
a document stating the name of the accused

Questions can arise when there are more nouns than modifiers, or more modifiers than nouns, or when modifiers do not appear right next to the nouns they modify.
Consistent Terms

Throughout a draft, use one term consistently to mean one thing. This rule seems easy to follow, but the following definition shows how thoroughly it can be broken:

. . . Unless the context clearly indicates a different meaning, “warehouse” may be used interchangeably with “elevator,” “storage house,” or “facility.”

The same problem appears here:

Community water supplies that serve a population of 10,000 or more individuals . . . shall analyze for total trihalomethanes in accordance with this part, . . . . Systems serving 75,000 or more individuals shall begin sampling and analysis not later than January 1, 1982.
Drafters make variations like these unconsciously. Variations often show up near the beginnings of sentences, which do not usually deliver new information and so get less of drafters' attention.

To keep from varying your terms, choose one of the terms available, try to use it consistently, and check your draft or have someone else check it for variations, especially near sentence beginnings.

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