1. The Fluid: The primary source of buoyant force is the fluid (liquid or gas) that an object is submerged in. The pressure exerted by the fluid on the object is greater on the bottom surface than on the top surface, resulting in an upward force called buoyancy.

2. Gravity: While gravity itself doesn't directly exert buoyant force, it's an essential factor in how buoyancy works. Gravity pulls the fluid downwards, causing the pressure difference between the top and bottom of the object that leads to the buoyant force.

Essentially, buoyancy is a consequence of the pressure difference in a fluid due to gravity, and that pressure difference is what exerts the upward force on the object.