I believe that Captains are paid more than First Officers (and Second Officers) for a number of reasons, some of which follow: 1) they've (usually) been working at the airline longer, and in those cases where they haven't, it's usually because the F/O or S/O either didn't want to, or couldn't make the upgrade; 2) because the Captain signs for the aircraft, he/she is more valuable to the company. As well, he/she usually is more knowledgeable in both company and flight operations; 3) Anyone who actually thinks that the Captain and First Officer do the same job, has never been a Captain. They might appear to be doing the same job, but I can assure you, that in the very vast majority of cases, they are not thinking of the same things at all. It's the same in military fighter operations. When I was a newbie, I thought I had the tougher job, hanging on the wing, light in the star, through all kinds of weather and attitudes. Then when I made element (and later flight) lead, I realized which was the tougher job. Same thing in commercial aviation.