In Chinese grammar, 一 (yī) and 也 (yě) can work as a pair around something to mean ‘not even one’ or ‘not at all’. The pattern is 一 + classifier (+ noun) + 也 + 不 (bù) or 没 (méi) + verb.
This 一……也 pattern can only be negative. The word immediately after 也 (yě) is always 不 or 没. So phrases such as ‘I ate one’ cannot use the 一……也 pattern.
一 (yī) + classifier + 也 (yě): not even one
一 and its classifier (a measure word, such as 口 (kǒu) for a mouthful) come before 也, and the noun that they count follows the classifier. Sentences with this structure express that not a single instance of something happened, occurred or existed.
Note that 一 + the classifier comes before 也 and the negated verb phrase. It is not placed after the verb phrase.
Leaving out the noun
The noun can be dropped when the it’s already clear in context what it is. In that case the structure is just 一 + classifier + 也. The classifier still has to match the implied noun, such as 件 (jiàn) for clothes or 封 (fēng) for letters.
Those example sentences use a clause first to show you the context, but those clauses are not required for the 一……也 to be grammatical. Some examples without the context setup:
For each of these, it must be clear in context what the speaker is referring to.
一次也没……过: never once
With 次 (cì), the classifier for occasions, events and actions, the pattern says that something has never happened, not even once. It is usually used with 没 and the experience particle 过 (guo), as in 一次也没 + verb + 过.
Note that 没 is used here because the sentence is about something that has not happened. Using 不 would not fit with 过.
一点儿也不: not at all
一点儿 (yìdiǎnr) means ‘a little’. In the structure 一点儿也不 + adjective or verb, it can express ‘not at all’ or ‘not a bit’. This is a common way to strengthen a negative.
一点儿也没 + verb is a similar structure, and expresses that something did not happen at all.
不 or 没 after 也
没 is for expressing past negatives, i.e. things that did not happen or have not happened, such as not eating something or not having been somewhere. 没 is also for negating having or existence. 不 is for negating states, feelings and current or timeless actions, such as something being expensive, liking something, or an action in a negative command.
Note that the two sentences about coffee use the same measure of 一点儿 ‘a little’ in different ways. The first coffee sentence uses that measure with 不 to express ‘not like at all’, while the second uses 没 to express ‘not drank any at all’.
一……也 summary
- 一 + classifier (+ noun) + 也 + 不 or 没 means ‘not even one’.
- 一 + classifier alone is used when the noun is already clear.
- 一次也没 + verb + 过 means ‘never once’.
- 一点儿也不 + adjective or verb means ‘not at all’.
- 没 is for what did not happen, while 不 is for states and feelings.
- The pattern is always negative.