I learned simple present tense is used for universal truths or facts. If I'm telling the story in past tense, and I have to say a fact, should I use simple present tense?
Example:
They ran from the tiger. Tigers are (or were?) fast animals.
I learned simple present tense is used for universal truths or facts. If I'm telling the story in past tense, and I have to say a fact, should I use simple present tense?
Example:
They ran from the tiger. Tigers are (or were?) fast animals.
You have to use the present because general truths are formulated using that tense; in this particular context of permanently valid truth, the use of the present tense is called STATE PRESENT.
timeless statements or eternal truths: proverbial, scientific, mathematical statements
Statements assimilated to timeless statements
1 not such an extreme of temporal universality: geographical statements and others of similar nature
2 restricted time span
(This answer is based on CoGEL, Quirk et al, 1985, § 4.5)