In the study of language one use of the noun inflection and related words is to refer to changes in the way a word or sentence is spoken. (For another use see Inflect (Disambiguation) and Inflection.)
Inflection (in this use) refers to a change in pitch (i.e., a rise or fall) in the speaker’s voice, such as the rise in pitch at the end of a sentence which turns what would otherwise have been a statement into a question, e.g., turns ’He’s going to be late’ into ‘He’s going to be late?’
The verbal phrases ‘to inflect up’ and ‘to inflect down’ mean, respectively, ‘to raise the pitch of one’s voice’ and ‘to lower the pitch of one’s voice’.
Inflection has other functions besides its use to indicate that the speaker is asking a question. Different forms of inflection may serve to express the speaker’s emotions: thus disappointment or sorrow may be expressed by lowering the pitch of the voice, especially at the end of a sentence (as in ‘We’ve lost’), expressions of fear characteristically involve a rise in vocal pitch, while expressions of anger involve a lowered vocal pitch.
Inflection should be distinguished from other features of speech which admit of variation, such as tempo (i.e., how quickly or slowly the words are spoken) and volume (how loudly or quietly the words are spoken). Tempo and volume are not forms of inflection, but distinct from it.
In some languages, e.g., Chinese, the particular inflection with which a word is spoken is integral to its identity, so that the same syllable or syllables spoken with different inflections have different meanings, i.e., are different words. For example, in Chinese the syllable da spoken with a rising inflection means ‘to answer’ or ‘to reply’, but spoken with a falling inflection means ‘large’ or ‘big’. When inflections serve in this way not to express the emotions or attitudes of a speaker but to determine the meaning of words, they are by convention referred to as tones. Thus Chinese has four tones: the first ‘high and level’, the second ‘rising moderately’, the third ‘falling, then rising’, and the fourth ‘beginning high and falling steeply’.