In linguistics, phonemes are the basic building blocks of the language, in terms of single sounds, like oh, i, baa, ge.  In addition to these phonetic phonemes, there is prosody, which is the so-called supra-segmental phonemes: stress, intonation, and pitch of the sounds.  In American English, we use supra-segmental phonemes to stress certain word, to denote a question, or to give some sort of added or changed meaning to a string of words.  For example, you could say: I LOVE you, to convey that you love, not hat, someone.  However, if you change the stress to I love YOU, that means that you love that person, not someone else.  In addition, if you stress the "I", as in : I love you, then, you might be implying that you, not someone else, loves that person.  Thus, we get three different meanings from a three-word string by altering the supra-segmental phonemes.

In Chines, there is not that sort of flexibility.  In Chinese, if you change stress, intonation,or pitch of one sound, you can change it into different words.  There are 4 basic pitch patterns, in the language: a high note, high-to-low, low-to-high, and high-low-high.  For example, consider the word Ma.  Ma with a high pitch is  used at the end of a sentence to make the sentence interrogatory.  Ma high-to-low is used to scold or curse someone.  Ma high-low-high means a horse.  And Ma low-to-high means hemp or jute.

This use of prosody to change the meaning of words can make learning Chinese difficult for westerners.  I know it makes it hard for me since I am used to the freedom of using stress and intonation to change the meaning of my sentences.