If the source of your comments or analysis is a book, then it is recommended to use the present tense, whether the author is still alive or not. This is similar to the standard practice of summarising the action of a book or film in the present tense.
If, in the Kant example, Kant later changed his mind, then of course the past tense is appropriate.
Here is an extract from the article on Verb tense consistency from the Online Writing Lab (Owl) at Purdue:
Controlling shifts in a paragraph or essay
General guideline: Establish a primary tense for the main discourse, and use occasional shifts to other tenses to indicate changes in time frame.
Hints:
- Rely on past tense to narrate events and to refer to an author or an author's ideas as historical entities (biographical information about a historical figure or narration of developments in an author's ideas over time).
- Use present tense to state facts, to refer to perpetual or habitual actions, and to discuss your own ideas or those expressed by an author in a particular work. Also use present tense to describe action in a literary work, movie, or other fictional narrative. Occasionally, for dramatic effect, you may wish to narrate an event in present tense as though it were happening now. If you do, use present tense consistently throughout the narrative, making shifts only where appropriate.
Source: Verb Tense Consistency
