th sound

Core Rule

The “th” sound is a defining feature of English phonology and appears in two forms: voiceless /θ/ and voiced /ð/. Both are spelled th, but they differ by vocal fold vibration. Mastering this contrast is essential for accurate pronunciation, listening comprehension, and natural fluency.

Articulation Guide

Place the tip of the tongue lightly between the upper and lower teeth. Keep the lips relaxed. For /θ/, push air forward without vibrating the vocal cords. For /ð/, maintain the same tongue position while activating voicing. Do not substitute /s/, /z/, or /f/—these are common learner shortcuts that reduce intelligibility.

Word Analysis

• enthusiast /ɪnˈθuːziæst/: The th is voiceless /θ/, clearly articulated before the stressed syllable.
• enthusiastic /ɪnˌθuːziˈæstɪk/: The same /θ/ sound appears in a longer word and should remain crisp, not weakened.
• theirs /ðeərz/: Here th is voiced /ð/, typical of demonstratives and pronouns.

Pitfalls to Avoid

Do not rely on spelling alone; th does not signal voicing by itself. Word-initial function words often use /ð/, while many content words use /θ/. In fast speech, avoid dropping the tongue placement, which leads to unclear or accented output.