What tense to use in arts and humanities papers? How to Write and Publish a Scientific Paper advises writers to use the past tense when they write about unpublished research (including the research their paper reports), and to use the present tense to write about research previously published in a primary journal. So, presumably, writers should use the past tense to refer within their paper.  

However, in a reply to this question, a user commented that he uses the present tense when he references within his paper. 


What tense should writers use when they refer within their paper? 
Do arts and humanities papers use tense differently than science papers do?
Verb tense often distinguishes a paper in the humanities from one in the
natural and social sciences.

Generally you would write in the present tense in the humanities (e.g. John Doe explains) and you would use the past tense in a humanities paper only for reporting historical events.

The UNC Writing Centre have a good webpage with examples that explain the three types of verb tenses (present simple, past simple, and present perfect) that they say account for approximately 80% of the verb tense use in academic writing.