Why is nirvana not mara? The term "non-duality" oft appears in Buddhist English language literature, both contemporary and in translation. e.g. it is sometimes claimed to be the cornerstone of Yogacara philosophy, and its assertion of "mind only", that no part of us exists independently of consciousness, but nevertheless it does tend to have some existence.

Obviously the term nirvana means buddhist liberation, that point at which the sage or saint (both words appear in the English language literature) has put out the suffering of samsaric existence, be that its elimination or a realisation that it is, in someway, already so extinct.

Mara is the personification of skillessness, a character that deceives e.g. the aspirant away from the holy life, and as such represents (in a sentient being) let's suppose something like the opposite of skillful means. 

I thought that nonduality often (if not always) means that opposing terms (good and evil, or illusion and reality) depend upon each other, by convention at least.

So, whether or not the last paragraph is correct, does the above not suggest that nirvana is mara?
There are four terminological divisions of nirvana, and none of them is mara.

Non-duality does not mean “that opposing terms depend upon each other”. Rather, we posit three types of dualistic appearances :


appearance of conventionalities
appearance of true existence
appearance of the apprehended object and the apprehending consciousness as two different substances


A consciousness that is free from the three is said to be “free from dualistic appearances”. By extension, the person who is the object-possessor knowing “in a non-dualistic manner” is also said to be free from dualistic appearances.

Here is an example: Conventional truths do not appear in the perspective of the wisdom directly realizing emptiness. True existence does not appear to the superior's exalted wisdom directly realizing emptiness. There is no appearance of the object and the consciousness as being to different substantial entities to that consciousness. Because the wisdom directly realizing emptiness is free from the three types of dualistic appearances, we say that he who directly realizes emptiness does so “in a non-dualistic manner”. He is free from dualistic appearances (as long as he abides in meditative equipoise on emptiness).

You are right to oppose mara to skillful means. Maitreya/Asanga's Ornament of Clear Realization, says: “The first application in skillful means is called application in skilful means which is victorious over the four mara-demons”. 

However, there are four maras:


The mara of the contaminated appropriated aggregates,
The mara of the afflictions,
The mara of the lord of death, and
The mara of the sons of gods. Only this last one is actually referring to a being—obstructing external forces creating obstacles to gaining the freedom of the first three maras. They are gods of the desire realm only—not of the form realm and formless realm. The god Garab Wangchub is posited as an example in the commentary.


Non-abiding nirvana is freedom from the four (and is the final true cessation), therefore it is not mara.