English has two sounds spelled "th": the voiceless /θ/ (as in "think") and the voiced /ð/ (as in "this"). Many learners know both sounds exist but struggle to predict which one to use without memorizing each word individually.
Here is a rule that covers dozens of the most common words in English: every common grammatical function word with "th" uses the voiced /ð/ sound. No exceptions in this specific group.
The Complete List of /ð/ Function Words
These are among the most frequently used words in English. Every single one uses voiced /ð/:
| Word | IPA | Type |
|---|---|---|
| the | /ðə/ or /ðiː/ | article |
| this | /ðɪs/ | demonstrative pronoun |
| that | /ðæt/ | demonstrative pronoun / conjunction |
| these | /ðiːz/ | demonstrative pronoun |
| those | /ðoʊz/ | demonstrative pronoun |
| they | /ðeɪ/ | pronoun |
| them | /ðɛm/ | pronoun |
| their | /ðɛr/ | pronoun |
| there | /ðɛr/ | adverb / pronoun |
| then | /ðɛn/ | adverb / conjunction |
| though | /ðoʊ/ | conjunction |
| thus | /ðʌs/ | adverb |
| than | /ðæn/ | conjunction |
| thereby | /ˌðɛrˈbaɪ/ | adverb |
| therefore | /ˈðɛrfɔːr/ | adverb |
| themselves | /ðəmˈsɛlvz/ | pronoun |
How to Make the /ð/ Sound
To produce /ð/:
- Place the tip of your tongue lightly between your upper and lower front teeth (or just behind the upper teeth).
- Push air through while vibrating your vocal cords.
- You should feel a buzzing sensation on your tongue and teeth.
A quick test: put your fingers on your throat. When you say /ð/, you should feel vibration. When you say /θ/, you should not.
Why Function Words Use /ð/
This pattern is not a coincidence. It reflects an important principle in English phonology: function words tend to reduce and blur in natural speech. The voiced /ð/ is slightly easier to produce in rapid, unstressed speech than the voiceless /θ/ because the vocal cords are already active from the previous voiced sound. Over centuries of use, the most frequently spoken words were shaped by ease of production.
Content Words Almost Always Use /θ/
By contrast, content words (nouns, verbs, adjectives) with "th" almost always use the voiceless /θ/:
- think /θɪŋk/, thank /θæŋk/, third /θɜːrd/
- through /θruː/, throat /θroʊt/, thread /θrɛd/
- therapy /ˈθɛrəpi/, theater /ˈθiːətər/, thesis /ˈθiːsɪs/
- math /mæθ/, path /pæθ/, faith /feɪθ/
The main exceptions are words derived from Old English roots that happen to be content words: breathe /briːð/, soothe /suːð/, teethe /tiːð/, loathe /loʊð/.
Practice Sentences
Read these aloud, making sure every "th" in function words is voiced /ð/:
- The students there finished their work.
- They said that this was the best solution.
- She is taller than her sister, and therefore faster.
- Though it was late, they stayed then left quickly.
Memory Tip
Here is the simplest way to remember the rule: if the word is a grammatical word (a word that connects or refers to other things rather than having its own concrete meaning), it uses /ð/. If it is a content word (a word with its own meaning you could look up in a dictionary as a concept), it almost always uses /θ/.
Because "the," "this," "that," "they," "there," and "then" are among the most common words in the English language, mastering the /ð/ sound in these words alone will significantly improve your fluency and comprehension.