Three different spellings, one single sound. 'Bird', 'her', and 'fur' look unrelated on the page, but their stressed vowels are identical. Learning this saves you from inventing three different sounds where English uses only one.
The Rule
When they are stressed and followed by R (or R plus a consonant), the spellings IR, ER, and UR all produce the same vowel: /ɜːr/. It is the tense, central vowel you hear in 'her'. The same sound also appears in some OR words after W (word, work) and some EAR words (learn, earth).
IR, ER, UR = /ɜːr/
The same sound in OR and EAR
Why This Helps
Instead of memorizing a new vowel for every spelling, you learn one target sound and attach three spellings to it. Make the vowel with your tongue in the middle of your mouth and your lips relaxed, then add the American R. 'Sir', 'her', and 'blur' should all rhyme.
Exceptions to Watch
The rule applies only when no vowel follows the R. When a vowel comes after, the sound changes: 'here' (/hɪr/), 'hero' (/ˈhɪroʊ/), and 'pure' (/pjʊr/) are not /ɜːr/. Also, unstressed ER at the end of words becomes the weaker /ər/ schwa, as in 'teacher' and 'water'.
Practice Tip
Say the rhyming set out loud: bird, word, heard, third, nerd, curd. For a related sound, see our guide to the schwa sound.