I think ''The ideas of the philosopher are based in reality'' is acceptable
Yes, it is another alternative. I've included it.
The primary version in English should be:
"The philosopher's ideas are based on reality."
my answer is " the ideas of the philosopher rely on the reality"(present)
The Duolingo answer Is: The ideas of the philosopher are based on the reality. (past tense) I believe that is incorrect
This is not past tense. The phrasal verb "to be based on" is conjugated with "to be" so "are based on" is the present tense.
We did not use "rely on" because it would be used for physical situations not ideas as in philosophy.
Despite alainPierrot's comment from two years' ago (which nobody responded to), "... based UPON..." is still red-screened. Could a moderator please consider adding it?
Yes, thanks it's been added. Sometimes we are not informed of the comments which is why we request learners to use the Report option and then post their comments here.