Copyright and stuff

OK, if I want to refer to a song or poem in a post, I understand that copying the entire song is not acceptable (unless I wrote it myself, in which case I wouldn’t generally give it to the Chicago Reader anyway).

Is it acceptable to copy a portion of it, with the appropriate cite? Like just the refrain or a couple of lines?

Is it acceptable to link to a site that provides it, knowing that it is doing so inappropriately? Or with total ignorance?

Hopefully I’m asking these questions in the right place, I’m still somewhat new at this.

Excerpts are acceptable, so long as they’re reasonably short and a reasonably small proportion of the total work. The laws are vague here, deliberately, I think, but I’d think that the refrain of a song, to use your example, would be OK.

I have no clue as to whether it’s acceptable to link to another site that’s violating copyright.

And, of course, the question is moot if the piece is sufficiently old (78 years after the author’s death, I think), or if the author has explicitly released the work into the public domain. Feel free to quote as much Shakespeare as you want.