"The author wrote" vs. "the author writes"
Solution 1:
Grammar Girl recently addressed this topic in "Present Tense in a Story." Her basic thesis was that the tense of the verb sets an expectation that may or may not adhere to the situation. If I say, "Her name was Susan," does that imply that it no longer is Susan? You might be setting someone up to think she's either dead or married since! For that reason, even if it is "right" it may seem wrong, because it connotes a change, even if technically it doesn't denote one. What Grammar Girl does not say is that English actually lacks the ability to properly express this condition.
The truth is that this situation calls for an aorist verb - one that began in the past and may or may not be continuing. Aorists are the "non-temporal" verb. They are unmarked in respect to time. They say "it doesn't really matter when this action occurred."
Greek uses this extensively - especially in the New Testament. English, like most Latin and Germanic languages lacks this, however. As such, either the past or present tense (or even a present progressive or past progressive) is valid, because we do not have a single case that covers both.
Solution 2:
In general the present tense is used when the author’s words are the subject of present discussion. So we might say ‘Schopenhauer writes that after your death you will be what you were before your birth, but there is no real evidence for that claim.’
The past tense might be used when an author’s words are being quoted, but no detailed discussion is expected, as in, for example, ‘Keats wrote that beauty is truth, truth beauty.’
In practice, however, there is often no hard and fast distinction, and the use of the two tenses is a matter of personal choice, depending on the circumstances at the time of speaking or writing.