Recently I've been reading up on the Pathfinder Slayer, and the Blood Reader talent fascinates me. It states that I can determine the remaining hit points of any living enemy, but it does not work on creatures that are not alive. Now, enemies such as Elementals who lack organs, do not bleed, and sometimes even lack a tangible form. They lack all of the hallmarks of life, except for mobility. So, in general, are Elementals and other extraplanars considered living creatures for Pathfinder?
Yes, they are alive.
Unlike most living creatures, an outsider does not have a dual nature
PS: Other systems may have differences on this, as my answer is based upon Pathfinder and D&D 3.x