the third-party

Writers often wonder whether to write third party, third-party, or (never) thirdparty. The core rule is simple: as a noun, use two words; as an adjective before a noun, hyphenate. Keep examples handy and pick the form that matches each sentence.

Quick answer

Use third party (two words) when the phrase is a noun: We hired a third party. Hyphenate third-party when it directly modifies a noun: a third-party vendor. Never write thirdparty in standard prose.

Noun (no hyphen): a third party, many third parties.
Adjective (hyphen before noun): third-party integration, third-party vendor.
Avoid thirdparty; it's nonstandard except as a brand or code token.

Core rule: noun vs modifier (fast check)

Ask whether the phrase names someone/thing (noun) or describes a noun (modifier). If it follows a verb or stands alone, it's a noun-no hyphen. If it sits immediately before another noun, hyphenate.

Subject/object (noun): We hired a third party.
Modifier before a noun (hyphen): a third-party vendor.

Wrong: I hired a third party vendor for onboarding.
Right: I hired a third-party vendor for onboarding.
Wrong: We asked a third-party to audit the data.
Right: We asked a third party to audit the data.

Hyphenation mechanics: why use the dash

Hyphens bind words into a single idea that modifies a noun. Without the hyphen, readers can misread which words belong together.

Put the hyphen when the compound appears before the noun it modifies. If the compound follows the noun, the hyphen is usually unnecessary.

Before a noun: hyphenate (a long-term plan, a third-party contractor).
After a noun: drop the hyphen (The plan is long term; the contractor is a third party).

Wrong: We hired a third party-contractor to assist.
Right: We hired a third-party contractor to assist.

Spacing and the single-word trap

Running the words together (thirdparty) creates a nonstandard token that most style guides reject. Use one word only for brand names, code identifiers, or deliberate trademarked forms.

If a product or URL shows a joined form, keep running text as third party or third-party according to grammar.

Never use thirdparty in reports, emails, or essays.
If a product is named ThirdParty, treat it as a proper name; avoid the form in descriptive copy.

Wrong: Thirdparty integrations are broken in the doc.
Right: Third-party integrations are broken in the doc.

Grammar edge cases: plurals, possessives, punctuation

Pluralize the noun as third parties. For a hyphenated adjective + noun, pluralize the main noun: third-party vendors. Possessives work best with simple rewrites when punctuation gets awkward.

Noun plural: third parties.
Adjective + noun plural: third-party vendors.
Possessive: the third party's response. Or rewrite: the response from the third-party vendor.

Wrong: Third-parties vendors were invited.
Right: Third-party vendors were invited.
Wrong: The third-party's deliverable is late.
Right: The third party's deliverable is late. (Or: The deliverable from the third-party vendor is late.)

Real usage by context: workplace, school, and casual

Match formality and clarity to context. Legal and workplace writing demands consistency; follow a contract or company style guide when provided. School work favors clear, conventional forms. Casual messages are forgiving, but correct hyphenation prevents confusion.

Legal/technical: keep hyphenation consistent across the document; follow defined terms in contracts.
School: use third-party sources (adjective) or a third party (noun) as appropriate for clarity.
Casual: choose the form that reads best while following the noun/adjective rule.

Work - Wrong: We need to notify thirdparty vendors about the outage. →
Right: We need to notify third-party vendors about the outage.
Work - Right: The third party will confirm insurance coverage.
Work - Right: Add a third-party vendor field to the procurement form.
School - Wrong: I relied on thirdparty sources for the literature review. →
Right: I relied on third-party sources for the literature review.
School - Right: The study engaged a third party to collect survey responses.
Casual - Wrong: Got a message from a thirdparty app about permissions. →
Right: Got a message from a third-party app about permissions.
Casual - Right: Ask a third party to pick up the package if you're out.

Try your own sentence

Test the whole sentence: does the phrase name someone/thing or describe a noun? Context usually makes the right choice obvious. Paste sentences into a grammar tool or keep a quick checklist handy.

Examples: common wrong/right pairs to copy

Swap the nouns (vendor, source, app, contractor) for your own term and keep hyphenation consistent with function.

Wrong: Thirdparty vendors must complete training before access is granted. →
Right: Third-party vendors must complete training before access is granted.
Wrong: I used a thirdparty source without checking its credibility. →
Right: I used a third-party source without checking its credibility.
Wrong: She is a thirdparty in the dispute and stayed neutral. →
Right: She is a third party in the dispute and stayed neutral.
Wrong: We prefer thirdparty solutions for quick integrations. →
Right: We prefer third-party solutions for quick integrations.
Wrong: The thirdparty's input influenced the decision. →
Right: The third party's input influenced the decision.
Wrong: Please followup with the thirdparty contact. →
Right: Please follow up with the third-party contact.

Fix your sentence: templates and quick rewrites

Decide noun or modifier, then choose a template. When possessives or plurals become awkward, rewrite to avoid punctuation problems.

Template (noun): I hired a third party to [do X].
Template (adjective): I hired a third-party [role] to [do X].
If possessive is awkward: the [result] from the third-party [role].

Rewrite:
Original: I hired a third party vendor, they will set up the CRM. →
Rewrite: I hired a third-party vendor to set up the CRM.
Rewrite:
Original: We relied on third party sources which seemed biased. →
Rewrite: We relied on third-party sources that appeared biased. (Or: The third-party sources appeared biased.)
Rewrite:
Original: The thirdparty's evaluation is attached. →
Rewrite: The third party's evaluation is attached. (Or: The evaluation from the third-party vendor is attached.)
Rewrite: Template swap: We used Acme Testing, a third-party vendor, for testing.

Memory trick and a 4-step edit checklist

Mnemonic: Noun = No Dash; Adjective = Attach Dash. Use this short rule to speed edits.

1) Identify function: noun or modifier?
2) If modifier and it precedes a noun → hyphenate.
3) If it follows a verb or stands alone → no hyphen.
4) Never join into one word; rewrite if possessive/plural is clumsy.

Checklist example: "We hired a third-party consultant" → Step 1: modifier? Yes. Step 2: before noun? Yes → hyphenate.

Similar mistakes to watch for

Apply the same function-based decision to other pairs such as follow up vs follow-up, set up vs setup, long term vs long-term, user friendly vs user-friendly.

follow up (verb) vs follow-up (noun/adjective)
set up (verb) vs setup (noun) vs set-up (modifier)
long term (noun) vs long-term (modifier)

Wrong: Please followup with the thirdparty contact. →
Right: Please follow up with the third-party contact.

FAQ

Should I hyphenate third-party?

Hyphenate third-party when it directly modifies a noun (a third-party vendor). If it's a noun on its own (We hired a third party), do not hyphenate.

Is thirdparty one word?

No. thirdparty as one word is nonstandard in running text. Use third party or third-party depending on function; reserve one-word forms for code or brand tokens only.

Which is correct: 'I hired a third party vendor' or 'I hired a third-party vendor'?

Use 'I hired a third-party vendor' because the phrase modifies 'vendor'. If the hired person is being referred to as a separate party, write 'I hired a third party.'

How do I form the plural?

Pluralize the noun: third parties. For a hyphenated adjective + noun, pluralize the noun being modified: third-party vendors.

What if my company style guide disagrees?

Follow your company or document style guide. If none exists, use the noun-vs-modifier rule consistently and add a brief note to the team style sheet.

Still unsure about a sentence?

Paste a sentence into a grammar tool or include it in your next message with context (work, school, casual). You'll get a ready-to-send rewrite and the hyphenation rationale.

Small hyphenation fixes keep documents clear and professional; a quick edit prevents misunderstandings.