Okay, let's imagine you have a bunch of toys. Some are big and some are small, some are loud and some are quiet, some are fluffy and some are smooth. And let's say you have a group of friends over to play with these toys.
Now, your friends might look at all of the toys and notice that some of them have some things in common. For example, all of the big toys might be vehicles like trucks or buses, and all of the small toys might be animals like dogs or cats.
This is kind of like what medium essentialism is all about. It's the idea that we can group things together based on the ways they are made or the materials they are made from. So, just like your friends noticed that some of your toys were vehicles and some were animals, medium essentialists might notice that some things in the world are made out of clay, or wood, or metal, or plastic, and group those things together.
Medium essentialism is a way of thinking about things that helps us understand how they are similar or different from one another based on the materials they are made from.