What is the difference between substitute and alternative ? In what cases we can use them?

Question

Answer

A substitute is something that temporarily takes the place of another thing.

Example: "The teacher is gone today, so there is a substitute teacher here instead."

An alternative is basically just a different option from a range of choices.

Example: "We use a lot of gas powering our house, maybe we should use an alternative energy source."

I hope this helps :)