In words that end with t or ed, the key is the preceding consonant sound. Some letters blend with the t and d so that the sounds are distinguishable, but some don't.
For example:
- the f sound causes the -ed to sound like a t: that's why stiffed rhymes with lift
- the k sound caused the -ed to sound like a t: that's why backed rhymes with fact
- the p sound caused the -ed to sound like a t: that's why wrapped rhymes with apt
- the s sound caused the -ed to sound like a t: that's why kissed rhymes with list
However:
- -ed and t sound different after l, which is why felled and belt do not rhyme
- -ed and t sound different after r, which is why barred and cart do not rhyme
- -ed and t sound different after n, which is why panned and rant do not rhyme
These aren't deliberate "rules" that need to be remembered; these are simply ways the sounds come out naturally. (It's worth paying attention to how similarly we pronounce some pairs of consonants, such as b and p, or t and d. Simply pronounce each one three or four times, and pay attention to how similarly your lips and tongue move.)
Some consonants don't figure into this discussion, because there aren't any words that end with sounds like:
- gt (to compare with, say, hugged)
- bt (to compare with, say, ribbed)