Inflection refers to the way we change the form of a word to show different parts of grammar such as voice, person‏‎, number, gender‏‎, mood, tense or case.

A simple example is when we change I to me depending on where it is used in a sentence. The person remains the same, the word changes.

I love you.
You love me.

Although some languages are highly inflected with complex inflection systems, English is fairly simple in this regard. For example, sometimes we add a possessive apostrophe to a word to show possession or an -s to a word to show it is plural.

John > John‘s
car > cars

Other times we add -ing to a word to make a different form of a verb:

feel > feeling
run > running

However, we’ll look at these in more detail below.

Note that when the inflection is on a verb, we refer to it as conjugation‏‎ while the inflection of nouns, adjectives‏‎ and pronouns‏‎ is called declension.

Pronouns

In English, we can find the most common inflections in pronouns which are declined for number (singular or plural) and case (whether they are subject or object, etc). They’re set out in this table:

See the main article to read more about Personal Pronouns‏‎.

Other Inflections

Aside from pronouns, we have these types of inflection in English:

• Possessive Apostrophe (‘s)
• Plural –s (houses, boys, churches, schools)
• Third person singular –s (He goes; She visits)
• Past tense –d, -ed or –t
• Negative participle –not/never
• -ing form of verbs (coming; going; walking; doing)
• Comparative –er (better; sooner; healthier)
• Superlative –est (best, soonest, healthiest)

More About Inflection

The grammarian Greenbaum explains inflections like this (from The Oxford English Grammar. Oxford Univ. Press, 1996):

Inflections are morphemes that signal the grammatical variants of a word; the inflectional -s at the end of ideas indicates that the noun is plural; the inflectional -s at the end of makes indicates that the verb is the third person singular, so that we say she makes but I make and they make. In addition, some affixes signal the part of speech to which a word belongs: the prefix -en in enslave converts the noun slave into a verb, and the suffix -ize converts the adjective modern into the verb modernize. 

in other words…

Inflectional Morphemes

Inflectional morpheme‏s‎ show grammatical information such as number, tense, possession, etc. For example:

number (singular/plural)

child – children

tense (verb form)

walk – walked

possession

Mary’s pen

However, there is no fundamental change in meaning when a word is inflected.

Where’s the Inflection?

Inflections in English are only found in suffixes (at the end of the word stem) and they are always attached to completed words. For example:

Boys

Mary’s

swimming

Note that in many other languages inflection occurs in prefixes (before the stem of the word) and sometimes in infixes (within the stem of the word).

Why Inflect?

In the early days of English the language was much more highly inflected. This inflection was used to show who was speaking and what they were talking about. However, over the years English has lost much of its inflection.

Nowadays what remains is still used to help us understand meaning. For example, inflection helps us to distinguish the subject-verb agreement‏‎ so that we write:

Everyone knows her and says that she is extremely smart.

instead of

Everyone know her and say that she is extremely smart.

Inflection also makes sure that person and number agree. For example, native speakers quickly recognize that The child are playing is incorrect since the subject is singular and the verb is plural, while The children are playing is correct.

Inflection & the TEFL Classroom

As you can see, inflection is an important part of language learning since conjugations and declensions can have a great impact on the meaning of an utterance and mistakes in inflection are easily noted.

However, this does not mean that it’s necessary to teach students inflection as such. It is probably better to simply teach the various rules as and when they arise in class. For example when students begin to study plurals you can explain that we make plurals in English simply by adding -s to the end of the singular word. There is certainly no need to go into what this -s is called (a morpheme) or anything deeper.

Likewise using the word declension in class is probably not called for.

In fact, the only word your class might benefit from knowing is conjugation.

Useful Links

Conjugation‏‎ in English – more on conjugation in English