Trouble With Tenses- Sequence of Tenses.

Which should you say?
Margaret said I owe her 100 dollars. Margaret said I owed her 100 dollars.
Traditional grammar, based on Latin, has taught that the second is preferable. The rule for reported speech went like this: if the main verb is past, the verb in the reporting clause must be too.
For English this simple is not correct. Certainly owed is fine example above, but – supposing I still do owe Margaret the 100 dollars – the form owe is perfectly acceptable.
In fact, there is a slight difference of emphasis between the two sample sentences. The first emphasizes the fact of owing; the second the fact of saying so. Things that are still considered to be true are likely to be reported by a present tense, and vice versa:
Copernicus discovered that the Earth went/goes round the Sun. Ptolemy believed that the Sun went round the Earth.
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