Once it makes a complete thought and has a subject and a predicate, it becomes a sentence. In this wise, it also starts with a capital letter and ends with a full stop, question mark or an ...

If it has one (subject or predicate), the other will not be present ... a phrase cannot normally function alone (cannot make a complete thought like a sentence), a clause can at times.

There are times when a clause constitutes a sentence. Once it makes a complete thought and has a subject and a predicate, it becomes a sentence. In this wise, it also starts with a capital letter ...