Thomas Aquinas believed that everything in nature has a natural tendency towards what is good for itself and the universe. He used the example of the four elements having inclinations to their natural places. This idea helps us understand that humans also have natural inclinations towards what is good for them. However, in our modern understanding, this concept doesn't fully align with how we see the world. While natural substances still show purpose in our world, it's not as broad as Aquinas thought.