Articles - Correct and Preferred Usage

AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Correct and Preferred Usage

The article a is used before the aspirate h (eg, a historic occasion) and nonvocalic y (eg, a ubiquitous organism). Abbreviations and acronyms are preceded by a or an according to the sound following (eg, a UN resolution, an HMO plan) (see 13.8, Agencies, Organizations, Foundations, Funding Bodies, and Others and 7.0, Grammar).

a hypothesis [h sound]

an ultraviolet source [u sound]

a WMA report [d sound]

a UV source [y sound]

a hematocrit [h sound]

an honorarium [o sound]

an MD degree [e sound]

an NIH grant [e sound]

a historic operation [h sound]

a historical reenactment [h sound]