A simple sentence is one independent clause that has one subject and a verb and expresses a complete thought. For instance, "yesterday Carla went to the doctor" is a simple sentence since it contains a subject (the NP Carla) and a predicate (yesterday went to the doctor). This is an independent sentence because it does not need another element to complete its meaning (see c). C is a dependent clause because it depends on the independent clause to complete its meaning (see b).
a) Yesterday Carla went to the doctor
b) Yesterday Carla went to the doctor because she had a headache
