-The scientist said (that) man cannot live without water.
It is written that we can't change the tense if it is a general truth, general facts, historical events and proverbs. Is that right? Can't we utter it like that?
-The scientist said (that) man couldn't live without water.
Tense changes in indirect speech | Grammaring
Could you please check this page?
No tense changes are made...
(a) if the reporting verb is in present, future or the present perfect tenses:
John says he loves you.
(b) if the reported words are always true:
The teacher told us that water boils at 100 degrees Celsius. (it still does)
Copernicus discovered that the planets move around the sun. (this is what we believe still today)
Ok. I know we can write them like this, but I would like to ask whether we can change the time or not. Because it is written as you have seen 'No tense changes are made...'
The writer of that article should have written, for (b), "No tense changes need be made" ..." or "Tense changes are often not made ..." That would have been more accurate.
Thanksssssss.... Because it doesn't sound bad to me either.
The water boils at 100 degrees Celsius.
The teacher told us that water boils at 100 degrees Celsius.
The teacher told us that water boiled at 100 degrees Celsius.
One 's' is enough for 'thanks'.
Last question for this.
Human beings cannot live without water
-The scientist said that human beings cannot/couldn't live without water.
It doesn't matter when the tense is not changed even if we use 'can-may-will', is that right?
It is OFTEN the case that we don't change the tense for reported speech. However, that doesn't mean that there is a rule that says "Never change the tense!"
It's not common to change it from "can't" to "could not" but neither 5jj nor I would say you were incorrect if you did so.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.