Inflection, intonation, accent are comparable when they designate a particular manner of employing the tones of the voice in speech.
Inflection implies change in pitch or tone; it often suggests a variation expressive of emotion or sentiment, and, usually, a momentary mood.
Intonation is often individual but it is seldom thought of as the result of a mood; it is applied to the rise and fall in pitch that constitutes what is called “speech melody” and that distinguishes the utterance of one individual or group from another.
In some languages (as Chinese), called “tone languages,” fixed pitch, or intonation, distinguishes the various meanings of single words. In a more specific sense, intonation often (as intone always) implies reciting or speaking religious matter (as a psalm or a prayer) in a singing voice, usually in monotone.
Accent denotes such manner or quality of utterance or tone as may distinguish a particular variety of speech (as one peculiar to a person, race, district, or class). Like the other terms in this group, it often suggests, and sometimes indicates, the speaker’s feelings.