had to
hatta
/ˈhætə/AssimilationReduction
In real speech
What happens to the sounds
The d before the voiceless t loses its voice and merges with it, and to weakens to /ə/: had to → “HAT-ta”.
When to use it
The past of have to: I had to go. Used in every style; written had to.
Casual → formal
Slang
hadda
Neutral
had to
Formal
was required to
Sound notes
Assimilation: neighbouring sounds change each other, e.g. t + y → “ch”, d + y → “j”.