The major word classes, nouns, verbs, adjectives and adverbs, can be characterised in terms of their morphological ('word-building') properties. Words that belong to the same class typically accept the same range of suffixes (endings). Moreover, there are suffixes that are characteristically used to form words of a particular word class.
Many nouns accept two different types of suffixes: the plural -s and the genitive -'s.
one girl - many girls
the girl's book
Both these morphological characteristics have important exceptions:
- A large subclass of nouns, referred to as uncountable nouns, do not accept the plural -s ending. Examples include furniture, money, information, and many others.
- The genitive -s is mainly attached to nouns that refer to animate beings, and not, for example, to nouns like gold, oxygen, demineralisation, etc.
Nouns can also be identified by the presence of a variety of noun-forming suffixes, which are used to form nouns from other classes of words. Examples include suffixes like -ion (with variants -tion and -ation), which form abstract nouns that typically refer to events or results of processes, as in denunciation, commission, starvation, sedimentation, etc.
Other noun-forming suffixes include -ity, -ment and -ance /-ence, which also form abstract nouns and are therefore quite common in academic writing.
A typical English verb has four different forms:
- the base form (found in dictionary entries), e.g. kill
- the third person singular present tense form, e.g. kills
- the -ed form, e.g. killed
- the -ing form, e.g. killing
The -ed form is used both to form the past tense and the past participle (which occur together with be in the passive, e.g. Bill was killed by a snake, and with have in the perfect, e.g. Bill has killed a snake). The morphological characteristics of a verb is often summarized by giving the so called principal parts of the verb; the base form, the past tense, and the past participle, in that order. For example, the verb kill has the following principal parts:
kill - killed - killed
For regular verbs, the past tense and the past participle are formed by the addition of -ed. However, an important group of verbs, the irregular verbs, form the past tense and the past participle in other ways, e.g. by varying the vowel of the base form, by using other endings, or by using forms not directly related to the base form. For example:
write - wrote - written
go - went - gone
swear - swore - sworn
Most dictionaries contain a list of irregular verbs. Since they are irregularly formed, they need to be learnt or looked up.
Here is a link to a very useful list of irregular English verbs at a web site called Englishpage.com. The web site is intended for (advanced) learners of English as a foreign or second language and was developed by professional educators. The site is free of charge, but users will be exposed to some advertising from other serious companies. In spite of these advertisements and the fact that there is a company behind this site, this appears to be the the best online irregular verb list available.
Prototypical adjectives can be inflected for comparison. For example, the adjective tall has the following three forms:
tall - taller - tallest
Adjectives with more than one syllable use more and most for comparison. For example:
important - more important - most important
Adverbs are often formed from adjectives by means of the suffix -ly. For example:
slow (adjective) - slowly (adverb)
The presence of -ly, however, is not sufficient to identify an adverb, as there are also adjectives that end in -ly. For example:
a sickly appearance
a leasurely walk
Moreover, quite a few adverbs do not end in -ly. For example:
soon now never always well fast
Some adverbs may be inflected for comparison. For example:
soon - sooner - soonest
early - earlier - earliest
It is sometimes difficult to distinguish adverbs and adjectives just on the basis of their form.