Why do the words ran to catch bus not make a sentence?

The words "ran to catch bus" don't form a sentence because they lack a subject.

Here's why:

* Subject: A sentence needs a subject, which is the person or thing performing the action. In this case, we don't know who or what is running to catch the bus.

* Verb: The words have a verb ("ran"), but without a subject, it's incomplete.

To make a sentence, we need to add a subject. For example:

* He ran to catch the bus.

* The children ran to catch the bus.

Now we know who or what is performing the action of running.