Some English learners -- and native English speakers -- mistake the past tense with the past participle.

For example, they may use the past participle when they are supposed to use the simple past, as in, "I seen the full moon." Or, they may use the past tense when they are supposed to use the past participle, as in, "I should have went to the store."

These mistakes generally only happen with irregular verbs since, again, the past tense and past participle of regular verbs are identical. They both end in -ed.