Chicago Style is for book publishing and lowercases only short prepositions. AMA Style is for medical publishing and follows journalism-style rules closer to AP Style.
Chicago Style capitalizes all major words and long prepositions while lowercasing short prepositions of four letters or fewer, articles, and coordinating conjunctions. It is the dominant style for American book publishing.
Chicago Style is required for most manuscripts submitted to book publishers, literary journals, and academic presses. Scholars in the humanities default to it.
Open Chicago Style converterAMA Style capitalizes major words while lowercasing articles, coordinating conjunctions, and short prepositions. It governs journals published by the American Medical Association, including JAMA.
AMA Style is required for submissions to major medical journals and most clinical research publications. Medical writers and clinical researchers are expected to follow it.
Open AMA Style converterChicago Style is required for most manuscripts submitted to book publishers, literary journals, and academic presses. Scholars in the humanities default to it.
Prepositions of five or more letters are capitalized. Short prepositions like in, on, at, by, and of remain lowercase.
AMA Style is required for submissions to major medical journals and most clinical research publications. Medical writers and clinical researchers are expected to follow it.
Prepositions of three letters or fewer are lowercased. Proper nouns, brand names, and drug names follow their standard capitalization throughout.
Choose Chicago Style for book manuscripts, literary journals, and humanities publications.
Choose AMA Style for medical journal submissions and clinical research publications.
The two styles serve different professional communities and are unlikely to come into direct competition. The choice is determined by the target publication.