tenses - Do I use "argued" or "argues"? Past or Present?

Peter Singer (who is still alive) wrote a paper in 1971. A student is now reading it and wants to make various references to it in her assignment.

Does she write, for example, "Singer argued" or "Singer argues"? Similar verbs would also be used in the paper. Argued is past tense and would appear to be used correctly when referring to a paper that was written in the past. However what is written and now being read still has currency, therefore introducing an argument for "argues"

What I would like to achieve is identify the/a explicit rule that dictates one over/or the other Then the student can apply it consistently throughout the assignment (and I will stop umming and ahhing every time and throw off the appearance of being all knowledgeable on these matters).