A kernel sentence is a simple declarative sentence that only has one verb and is written in the active voice. It does not have any helping verbs or conjunctions that would alter the mood and the subject carries out the action in the verb. Kernel sentences do not have polarity either, which means that the word "not" would never appear.
An example of a kernel sentence is "The man started the car." The only significant words in the sentence are the subject, verb and the direct object (car). Sentences that contain adjectives, infinitives or gerunds are not kernel sentences; rather, they have combined two kernel sentences into a larger idea. For example, the sentence "This is a red car" combines the two kernel sentences "This is a car" and "The car is red." The sentence "I heard them ringing the doorbell" combines the two kernel sentences "I heard them" and "They were ringing the doorbell." Finally, the sentence "I like to eat" combines the kernel sentences "I like" and "I eat." The purpose of identifying and studying kernel sentences is to reduce the use of language down to its most basic ideas. Seeing how these ideas combine to make more complex ones is useful when understanding the structure of a language.