The two terms you are using here are later developments in literature. Marxism is primarily a political term, which when applied to literature, has to have more than just a business connection – it must incorporate the concepts of ownerships of the means of production, etc. Bartleby, while it does take place in a business world, does not deal with the distribution of wealth, etc. As for existentialism, this much overused philosophical term/concept requires a discussion of whether existence precedes essence, that is, whether we are acting out a previously designed project or are inventing ourselves (and humanity) as we make choices. While Bartleby may appear to be questioning his place in the structure of the free enterprise system, he is not questioning whether he is part of a previously concocted plan; neither of these approaches will bear analytical fruit, and both will move the reader away from the piece’s main point: What would happen if a man abandoned the apparently volunteer act of making choices? What if his choice was “I prefer not to” make choices any more? It is a very penetrating point of view, one that many feel puts light on Melville’s Moby Dick. But it is a mistake to see “Bartleby the Scrivener” as some sort of precursor to post-modern trends.