49 CFR § 171.9 - Rules of construction.

---
identifier: "/us/cfr/t49/s171.9"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "49 CFR § 171.9 - Rules of construction."
title_number: 49
title_name: "Transportation"
section_number: "171.9"
section_name: "Rules of construction."
chapter_name: "PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "HAZARDOUS MATERIALS REGULATIONS"
part_number: "171"
part_name: "GENERAL INFORMATION, REGULATIONS, AND DEFINITIONS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "49 U.S.C. 5101-5128, 44701; Pub. L. 101-410 section 4; Pub. L. 104-134, section 31001; Pub. L. 114-74 section 701 (28 U.S.C. 2461 note); 49 CFR 1.81 and 1.97."
cfr_part: "171"
---


# 171.9 Rules of construction.

(a) In this subchapter, unless the context requires otherwise:

(1) Words imparting the singular include the plural;

(2) Words imparting the plural include the singular; and

(3) Words imparting the masculine gender include the feminine;

(b) In this subchapter, the word: (1) “Shall” is used in an imperative sense;

(2) “Must” is used in an imperative sense;

(3) “Should” is used in a recommendatory sense;

(4) “May” is used in a permissive sense to state authority or permission to do the act described, and the words “no person may * * *” or “a person may not * * *” means that no person is required, authorized, or permitted to do the act described; and

(5) “Includes” is used as a word of inclusion not limitation.

[Amdt. 171-32, 41 FR 15996, Apr. 15, 1976, as amended by Amdt. 171-32A, 41 FR 40630, Sept. 20, 1976; Amdt. 171-121, 58 FR 51528, Oct. 1, 1993; 75 FR 60338, Sept. 30, 2010]