We use reported speech to tell a person (Julia) what another person (Sam) has said. Depending on when Sam made his statement, we adjust the tense of the reported speech.
Sam: I like pineapple.
to Julia: Sam says he likes pineapple.
When the reporting verb, in this case “says” is in the present tense, the following verb (likes) is typically also in the present tense.
This would be appropriate to use when Sam has just made this statement, and someone standing right next to him, Julia, did not understand. If the reporting verb is in the past tense, then the following verb is also in the past tense.
Sam: (said last week) I like pineapple.
to Julia: Sam said he liked pineapple.
Sam: (said last week) I am going to the concert on Saturday.
to Julia: Sam said he was going to the concert on Saturday.
To form reported speech in the correct tense, there is typically a back-shift in tense from the direct speech to the reported speech.
Some modal verbs do not change when used in reported speech. These words are “might, would, could, should, used to”. Other modal verbs will change to the following: