If you ask a 7-year-old how to make an English verb into the past tense, he or she will probably tell you, “Just add an -ed to the end.” The child may not have learnt that some verbs need just a t to become past tense. Others are even more complicated than that.
In the case of learn, you have two options. You may use the standard past tense (learned), or you may save a letter and finish off the verb with more punch: learnt.
Indeed, many verbs are available to take either an -ed or a -t to become past tense. Some examples: burned/burnt; dreamed/ dreamt; dwelled/dwelt; kneeled/knelt; leaped/leapt; smelled/smelt.
Other verbs cannot under any circumstances take on an -ed to go past tense.
You haven't builded a house; you’ve built one. You haven't shooted that man; you've shot him. You haven’t sleeped the day away; you’ve slept way too long.
Then there are the deeply strange verbs that become past tense in ways you could never predict. Go becomes went. See becomes saw. Eat becomes ate. Teach becomes taught.
Finally, there are words that may be either past tense or present. The past and present tense look the same on the page. Whether it is happening now or happened yesterday, we bet, cut, hit, put, quit, let, spread, and read.
The most common past-tense error has nothing to do with -ed or -t. It has to do with the past tense of lay and lie. Lay requires an object. You lay your key on the table. To make this past tense, you change lay to laid.
Lie, on the other hand, does not need an object. Your key lies on the floor. To go past-tense with that, you use lay, as in, “Yesterday, my key lay on the floor.”
Hope I haven't spoilt your day.