Intrusion is the insertion of a sound between two words to ease the transition from one vowel to the next. It is a natural feature of connected speech, functioning alongside linking, elision, and assimilation. The inserted sound is not represented in spelling and is not deliberate; it arises from the articulatory movement between vowel positions.
Intrusive /r/: Inserted after words ending in /ə/, /ɑː/, /ɔː/, or centring diphthongs when the next word begins with a vowel. Common in non-rhotic accents (RP, Australian English).
Distinguished from linking /r/, where the r exists in the spelling (e.g., "far away" /fɑːr əˈweɪ/).
Intrusive /j/: Inserted after front vowels (/iː/, /eɪ/, /aɪ/) before a following vowel.
Intrusive /w/: Inserted after back rounded vowels (/uː/, /əʊ/, /aʊ/) before a following vowel.