Tone changes

[xuechengfeng]

Sorry if this has been discussed ten billion times, but I found nothing on the search. When do you change the tone? I know, I know. . . pretty broad.

But for example. . .

朋友

Peng2you3, but I see the 友 go from you3 to you5.

Also, are there certain situations where you are supposed to change it? I find it very difficult to go from tone 1 to tone 2, for example. . .

单独

Dan1du2.

Do you actually pronounce it like that, or is this another word where the last character is changed to a neutral tone?

Dan1du5 seems much easier to pronounce than Dan1du2 (to a foreigner @ least).

[amego]

The fifth tone is known as 轻声, neutral tone. Well I can't provide much info on the 5th tone sandhi 'cos Singaporean don't seem to use the 5th tone. So much so that i don't really know the 5th tone! Haha.

Anyway the general case is

A3B3---->>>>A2B3 e.g. 老鼠 lao3 shu3 ----->>>> lao2 shu3. And tons other more.

See here and here.

[NYC]

Pronouncing you3 as you5 is not due to tone changes per se but because friend is an common/everyday/colloquial word and these often have neutral tones (ma1ma5, ba4ba5, chuang1hu5, etc.) on the second syllable. In the case of 姐姐 however I believe it can be pronounced either jie3jie5 or jie2jie5 since in this case (3+3>2+3>2+5) a tone change is involved.

In 单独, I believe it is pronounced dan1du2 and not dan1du5 (are neutrals more common in nouns?), however in colloquial speech it may sound that way. Another thing about neutral tones, their pronunciation does differ slightly depending on the preceding tone (search for pitch contours). Yes in my opinion tones are the hardest thing in Chinese to learn (apart from the writing system).