In my world, there are two different magic systems. One involves making a pact with a god or spirit to agree to do a specific thing in exchange for power.
The other involves using special spells and rituals to achieve the same magic result.
How can I reasonably explain how one world can have two different magic systems?
Note, in case of the first system, the price comes out of what ever contract you made to get your power.
In the second system, magic draws life energy from the user, and over-use can result in death.
Both systems developed in the same society, but the second one formed first (no one knows how) and was passed down the generations; it is most popular among the rich and/or city dwellers.
The first system formed much later and is most popular among the poor and/or farmers.