B737-700
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 63; Flight Crew Total 8300; Flight Crew Type 63
Situational Awareness; Confusion
Deviation - Track / Heading All Types; Ground Incursion Taxiway
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Human Factors
We had taxi instruction to taxi to 22R intersection W. Shortly thereafter they amended instruction for takeoff 22 R full length. That became confusing with crossing a runway; going through hotspot; etc. We lost situational awareness in the process. We were cleared for takeoff quite some time prior to getting to the runway. The Captain lined up on taxiway papa. Having already been cleared for takeoff the Captain had already advanced the thrust levers up a bit and I took aircraft control. I slowly advanced the thrust levers and before pressing TOGA (Take-Off / Go-Around) I realized we were not on a runway but a taxiway. I stopped the aircraft immediately. ATC came on as I was stopping telling us to stop. They then told us to taxi on to 22R back taxi and we were cleared for takeoff.
B737 First Officer reported the Captain lined up for take off on a taxiway and started departure roll.