First class constraint

Okay kiddo, so have you ever played with building blocks? Imagine you have a big pile of blocks in front of you and you want to build a really cool structure. However, there are some rules you have to follow when building with blocks.

Now let's pretend that these rules are like equations that you have to follow. And just like how you can't build a structure that violates the rules of building blocks, in physics, we can't have equations that don't make sense because they violate the rules of nature.

Sometimes, when we try to make equations that describe the rules of nature, we end up with some weird equations that don't make sense. We call these "first class constraints".

Now, just like how you can't have a block structure that violates building rules, we can't have an equation that violates the rules of nature. So when we come across a first class constraint, we have to find a way to fix it.

Think of it like having a block that doesn't quite fit in with the rest of your structure. You have to figure out how to adjust the other blocks so that the structure still makes sense.

Overall, first class constraints are like little puzzles that we have to solve when making equations in physics. We have to make sure everything fits together nicely, just like building a cool structure out of building blocks.