Third tone sandhi: not the shape you were taught

Every course draws the third tone the same way: a line that dips to the bottom of your range and climbs back up. It is printed as 214 on the five-level pitch scale — start at 2, fall to 1, rise to 4.

That diagram is not wrong. It is just describing a situation you are almost never in.

The shape is what a syllable does alone

The full falling-rising contour appears when a third-tone syllable is said in isolation — one word, no neighbour, often at the end of a sentence. Drill a single syllable and you will hear it. Say a sentence and it mostly disappears.

In running speech the third tone usually stops halfway. It falls to the bottom of the range and stays there. Teachers call it the half third tone, and it is the version you hear most of the time. The rise is not a defining feature of the tone; it is what happens when the voice has room and time to come back up.

This matters because of how it is taught. A learner drills 214 in isolation, memorises the rise as the identity of the tone, then cannot find the tone in real speech — because in real speech it is not there.

Second tone or third: how to tell them apart

Ask a learner how to tell the second tone from the third and you will hear: the second is high, the third is low.

In real speech they sit in the same part of the range, and that description falls apart. Both can end up rising. Both can sit low. Height is not the difference.

The difference is when the contour turns. The second tone rises from the start — it begins in the middle and climbs, and the movement is upward from the first moment. The third tone keeps falling first, sits at the bottom, and only then, if there is room, comes back up. Two contours can reach the same place and still be unmistakable, because they get there in a different order.

If you are trying to hear the difference, stop listening for how high the syllable ends. Listen for whether it went down before it went up.

This is not a teaching metaphor we invented for an article. It is the measurable property: the timing of the turning point separates the two tones far more reliably than pitch height does, and it is what a pronunciation scorer has to look at if it wants to be right about which tone you produced.

Sandhi is the rule people worry about, and it is the easy one

Two third tones in a row do not both stay third. The first becomes a second tone.

• 你好 is written nǐ hǎo and said ní hǎo
• 很好 is written hěn hǎo and said hén hǎo
• 手表 is written shǒu biǎo and said shóu biǎo

The writing does not change. The pinyin in your textbook keeps the original tone marks, and you are expected to apply the rule yourself when you speak.

Learners find this alarming when they meet it, and then it turns out to be the most mechanical part of the whole system: two third tones adjacent, the first one changes. There is no list of exceptions to memorise.

The genuinely awkward case is three in a row, where the grouping decides the result. 我很好 — I am fine — has three third tones. It is normally said wǒ hén hǎo: the middle syllable groups with the last, that pair applies the rule, and the first syllable is left alone. Change how the phrase groups and the result changes with it, which is why this is a rhythm question rather than a spelling one.

Two more changes that are not third-tone sandhi

They are usually taught alongside it, and mixing them up is common.

不 (bù) becomes bú before a fourth tone. 不是 is bú shì, not bù shì. Before any other tone it stays bù.

一 (yī) is the busier of the two. Alone or at the end, it is yī. Before a fourth tone it becomes yí — 一个 is yí gè. Before a first, second or third tone it becomes yì — 一天 is yì tiān.

Neither of these has anything to do with the third tone. They are separate rules that happen to live in the same chapter.

What to do with this

Three things change if you take the above seriously.

Drill the half third tone, not only the full one. If every third tone you have ever produced had a rise on the end, you have practised the rare version and skipped the common one.

Judge second versus third by the turn. When you cannot tell which one you heard, ask whether the voice fell before it rose. That question has an answer; was it high or low frequently does not.

Apply sandhi out loud, and expect the page not to help. The text keeps the original marks forever. The rule lives in your mouth, not on the page.

Why we are writing this

We are building a pronunciation trainer, so we read the reviews of everything in this category. One of the most-installed pinyin apps carries a review, in Chinese, saying that every third-tone reading in it is wrong — that they all come out sounding like second tones.

That is a harsh thing to say about a reference tool, and it points at something real: the third tone is where pronunciation material most often goes wrong, in the apps as much as in the textbooks. It is the tone whose textbook diagram describes the exception rather than the rule.

You can hear all five contours, drawn to one pitch scale, on the tones page, and look up any syllable in the pinyin table.