It’s a complex issue, not made easier by websites that suggest there is a clear set of rules for the so-called ‘sequence of tenses’
Let’s look at two of the points.
To state a general truth, use the present tense: The Deists believed that the universe is like a giant clock.
The use of ‘believed’, past tense, suggests that the person who created this sentence may not believe that the universe is like a giant clock (i.e this is not a universal truth). That is why the sentence is much more likely to be: The Deists believed that the universe was like a giant clock. Of course, if there are still Deists who believe this, then we can report this as: The Deists believe that the universe is like a giant clock. That, however, is not a universal truth but a astatement about a current situation.
George: I am going to London next year, and I am not coming back!
Jessica: I don't care about it. I have already known that you are going to London next year again. You are always telling the same story!
This is faulty from the beginning. I have already known is unnatural. We’d say: I already know or I already knew.
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