Many English words can be broken into different morphemes, units of meaning. These morphemes can be either free or bound. In the word "cats", we have two morphemes. The first is the free morpheme "cat" and the second is the bound morpheme -s. A free morpheme can occur in isolation and a bound morpheme cannot. The bound morpheme -s cannot occur in isolation but speakers know that it conveys the meaning of plurality.
The word "disappointment" can be broken into three morphemes: dis + appoint + ment. It is also possible to construct a word tree to show how the three morphemes combine with one another. By comparing other words with the prefix dis- and the suffix -ment, we can determine the order in which they combine. The prefix dis-occurs in verbs such as dislike, disregard and distrust and attaches to verbs. The suffix -ment occurs in nouns such as government, improvement and development. It also attaches to verbs.
The word "disappointment" can combine in one of two possible ways. The solution is either disappoint + ment or dis + appointment. The first possibility combines a verb with the suffix -ment. This is the pattern in words such as improvement and development. The second solution combines the prefix dis- with nouns. However, this is not correct. The prefix dis- does not attach to nouns but rather to verbs such as "dislike" and "distrust". As a result, we reject this solution and choose the former. The rule is that the prefix dis- attaches to verbs and the suffix -ment also attaches to verbs. Therefore, the verb disappoint attaches to the suffix -ment. We can illustrate this as follows:
dis (Af) + appoint (V) V + -ment (Af) = disappointment (N).
The symbol Af stands for affix. This is a convenient term which can refer to either a prefix or a suffix.
With nouns such as "worker", "farmer" and "painter", it is clear that they consist of two morphemes, a noun and an agentive suffix -er. This suffix creates nouns known as agents which are introduced by the preposition "by" in passive sentences.
Less clear, however, is the classification of the root. Is it a noun or a verb? The words "work", "farm" and "paint" function as both nouns and verbs.
Evidence in support of the answer can be found in other words. The nouns "singer", "seller", "buyer" and "teacher" consist of roots which are verbs rather than nouns. Therefore, we can analyze the roots of words with the agentive suffix -er as verbs.
In the study of English morphology, the order in which morphemes combine with one another is not always immediately obvious. By comparing words with the same morphemes, though, it becomes possible to determine the order of morphemic combinations. In other cases, the classification of a root is not immediately clear. However, this can be determined by locating other words which belong to only one grammatical category. English morphology is really a very fascinating study of word formation in English.