Morphemes are used to analyze the development of language via the Mean Length of Utterance (MLU).
Language Analysis: Another use of Morphemes, not by the child this time but by professionals, is to evaluate the development of a childÅs language.
Most people use a gross rule of thumb based on words. If my child is one year old, he should be speaking, on the average, in one word sentences.
If he is two years old, he should average two word sentences. The three year old should average at least 3 word sentences.
For example, he might say, "Doggy's toys busted," which is a 3 word sentence.
Professionals, however, consider words to be too broad a unit to be very discriminative. Hence, they count the mean length of utterances in terms of both Bound and Free morphemes (MLU).
Hence the sentence, "Doggy's toys busted," would be considered to be 6 morphemes long.