"Hope springs eternal in the human breast:

Man never Is, but always To be blest:"
what's the name of the poem or essay by alexander pope that this is from? Is it called "An essay on a man"?

Yes.

I've seen it listed as any of the following:

An Essay on Man
Essay on Man
The Essay on Man

I think what Pope named it is "Essay on Man" -- no The or An in front.

http://www.google.com/search?q=essay+on+man&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7SUNA

Yes I have seen it here too... An Essay on Man

Essay on Man
The Essay on Man

thanks very much you guys

You are Welcome I have something else you can have once I find it for you.

The lines you mentioned are indeed from Alexander Pope, but they are not from "An Essay on Man." They are actually from his poem called "An Essay on Criticism." "An Essay on Criticism" is a didactic poem written in 1711, where Pope provides guidelines and principles for good literary criticism. The famous lines you quoted are found in the section on the characteristics of a good critic.