Natural inclination is the inner drive that pushes living things to act in certain ways. Aquinas believed that natural agents, like animals and plants, have this inclination to guide their actions towards specific goals, even though they may not consciously know these goals. He thought that this inclination comes from a higher power, like God, who gives them their nature and purpose. In essence, natural inclination is what makes living things do what they do, even if they don't fully understand why.