aught / naught / nought / ought
Zero, nothing, and duty.
Ought is the verb of duty: You ought to go. Naught means nothing: came to naught. Nought is the British spelling of that naught, and also a name for zero. Aught can mean zero in aughts for the years 2000–2009, or, in older English, “anything.” Do not write ought for zero, or aught for duty.
Examples
UseYou ought to call.
UseThe plan came to naught.
Usethe early aughts
AvoidYou aught to call.