# Rules of construction.

**Citation:** 49 CFR 171.9  
**Type / status:** regulation / current  
**Agency:** Pipeline and Hazardous Materials Safety Administration  
**Effective:** 2026-08-18  
**Published:** Not stated

(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 

## Document text

(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]

## Provenance

- Official: Yes
- Source: <https://www.ecfr.gov/on/2026-08-18/title-49/section-171.9>
- Source ID: `ecfr`
- SHA-256: `48c4f6a020d5481f10c121a3de9a37303a396c2730e387a43c6fa3e2700b23c4`
- Retrieved: 2026-08-20T05:45:53.607Z
- Exported: 2026-08-22T15:00:09.090Z
- Document slug: `49-cfr-171-9`

### Source metadata

```json
{
  "cfrTitle": 49,
  "part": "171",
  "section": "171.9",
  "subpart": "Subpart A—Applicability, General Requirements, and North American Shipments",
  "corpusVersion": "2026-08-18",
  "jurisdiction": "US"
}
```