---
kind: "section"
citation: "49 C.F.R. § 171.9"
title: "49"
number: "171.9"
heading: "Rules of construction."
url: "https://uscodex.org/cfr/49/171.9"
---

# §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.

## Notes

### Amendments

[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]

### Authority

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.

### Amendments

[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]