Every writer eventually stares at a headline and wonders whether "The" should be "the." The question hides a real decision: sentence case and title case aren't just two spellings of the same thing — they signal different contexts, follow different rules, and are handled differently by every style guide. Picking deliberately beats picking randomly.
The difference in one look
Sentence case capitalizes only the first word of the heading (plus proper nouns): How to train your dragon. Title case capitalizes the first word and every "major" word after it: How to Train Your Dragon. Same words, different machinery underneath.
| Sentence case | Title case |
|---|---|
| The complete guide to payment security | The Complete Guide to Payment Security |
| Why your email keeps bouncing | Why Your Email Keeps Bouncing |
| A memo from the CEO of Acme Corp | A Memo From the CEO of Acme Corp |
| Ten rules for better headings | Ten Rules for Better Headings |
What the style guides say
There is no single authority — there are several, and they disagree in the details:
- Chicago Manual of Style — title case for book and article titles; the standard reference for what counts as a "major" word.
- AP (Associated Press) — title case for headlines, but with its own capitalization rules (e.g., words under four letters often stay lowercase).
- APA / MLA — title case for reference titles in academic work.
- Web and product design systems — overwhelmingly sentence case for page titles, buttons, and navigation. Major platforms' style guides recommend it explicitly.
Notice the split: publishing and academia standardized on title case; software standardized on sentence case. That pattern tells you most of what you need.
Why software teams chose sentence case
Three practical reasons, all about friction. First, readability: a wall of capitals slows the eye, and interfaces are skimmed, not read. Second, proper nouns stand out — in sentence case, "Upload your Google Drive files" makes "Google Drive" pop; in title case every word shouts, so nothing does. Third, fewer arguments: title case has endless edge cases (Is "Is" capitalized? What about "vs."? Four-letter prepositions?). Sentence case has almost none. When a design system covers thousands of strings, that simplicity compounds.
How to title-case correctly (when you must)
When title case is the requirement, the working rules are: capitalize the first and last words always; capitalize nouns, pronouns, verbs, adjectives, adverbs, and subordinating conjunctions (because, although, if); lowercase articles (a, an, the), coordinating conjunctions (and, but, or), and the to in infinitives. Short prepositions are the battleground — Chicago lowercases them, AP capitalizes words of four letters or more. Whichever convention you follow, apply it the same way every time.
The classic traps: Is and It are always capitalized (verb and pronoun), What If Cats Ruled the World is right even though "the" is small, and hyphenated compounds capitalize both halves (Self-Driving Car) in most styles.
The only rule that actually matters
Consistency beats correctness here. A blog where one post is "How To Split A PDF" and the next is "How to split a PDF" looks broken even to readers who couldn't name the rule. Decide per surface — sentence case for product UI and blog headlines, title case for whitepapers and book references is a common split — write it down, and hold the line. If you're converting a batch of titles by hand, a quick check of each one in the WordlyCount counter keeps length discipline while you fix capitalization; for more on the punctuation decisions inside those titles, see the Oxford comma guide and em dash vs. en dash vs. hyphen.