In a recent e-mail, someone wrote What am I suppose to do?
That should be supposed, obviously – but was it a typo or a more serious error?
It could just be a typo, or else one of those spellings based on oral information only.
In colloquial speech, the final –d can sometimes drop off. (Dad said you’re not s’pose to do that!)
It clearly needs the past-tense ending, though. One is assumed, presumed, supposed or thought to do or have done something.
Similar is used, as in We used to rent videos but now just watch Netflix. The final D in used may also get lost in speech.
But use in that context could actually be correct. To use to do something, meaning to be in the habit of doing, is well-established usage. Archaic, though:
‘In that Season of the Year when the Water uses to be lowest’ (1726)
‘All delights which use to crown princely banquetings’ (1819)
Interestingly, this is still current in Caribbean English:
‘How she uses to dress’ (Dictionary of the English/Creole of Trinidad & Tobago (2009, citing 1959)