Tonguez said:
I'd rule too alien to reason with but they do understand the concept of self-preservation and that can be used as a bargaining point
eg a Fire Elemental knows that fire needs to consume fuel and oxygen in order to survive, it also understands that water and/or sand etc can quench its flame (self-preservation)
A clever PC able to speak Ignum (iirc) then needs to work out how those notions can be used
a water elemental understands the concepts of stagnation, pollution and becoming a bog so might be persuaded to attack the pollution causing wizards tour which is pouring alchemical sludge into the local fishing pond...
I'd run with this one. An Elemental would think of the world in terms of its element, and associated concepts.
A Fire Elemental's understanding of the world would be limited to concepts of related to fire. What burns well, what is hot, what kills fire, that sort of thing. Given the nature of fire, they'd also be constantly moving and in a hurry.
An Earth Elemental would have no sense of time a mortal could comprehend, being composed of rock and earth, and would see things as land or un-land, hard and not hard. They'd think in geological terms.*
A Water Elemental would understand depth, motion and vastness, but they'd probably be one of the most alien. Their idea of time would be bizarre to us, given the nature of water.
An Air Elemental would also understand travel, but would have no interest in anything that doesn't spend most of its time in the air. To them, it's there and then it's not, as they move on. While they're also theoretically ageless, their concept of time would be closer to our own, given that an Air Elemental never stops moving.
*
Had a great time trying to talk to an awakened rock in a Living Greyhawk game last night. Very well written encounter, the rock simply could not understand time, even when we tried to put in terms of how many times the sun had set. Its response was "I became me, he came, he went, he returned and went again, then you came."