@tanguatlay,
Quote:He said, "I'll go to the library tomorrow."
He said he would go to the library the next day/the day after.
Am I right to say that both phrases can be used in reported speech?
There are no rules specific to reported speech, Tan, that come ahead of common sense, of meaning.
It's important to establish
when the speech is being reported.
[Imagine it's Monday] A: "I'll go to the library tomorrow."
B: [reporting A's speech, it's still Monday] He said he would go to the library tomorrow.
In this situation, neither
the next day/the day after sound natural.
He said he would go to the library
the next day/the day after.
Both of these, underlined, sound like somebody reporting speech some time after it occurred, say as in a trial, where an actual day had been established and understood.
A: He said he would go to the library on Saturday, September, 23?
B: No, he said he would go there the next day/the day after that.