as does

### Rule 1: Use "as does" when the subject after it is **singular** ( one thing )
- *His English improves, **as does his confidence**. *
→ "his confidence" = singular → **does**
- *Her accent is getting better, **as does her pronunciation**. *
→ "her pronunciation" = singular → **does**
- *Their interest in reading grows, **as does their motivation**. *
→ "their motivation" = singular ( motivation is one thing ) → **does**
- - -
### Rule 2: Use "as do" when the subject after it is **plural** ( two or more things, or a compound subject )
- *His English improves, **as do his confidence and his writing skill**. *
→ two things ( confidence skill ) → **do**
- *Their interest in reading grows, **as do their motivation and their vocabulary**. *
→ two things → **do**
- *The students' grades rise, **as do their study habits**. *
→ "study habits" is plural ( habits ) → **do**
- - -
### The tricky case: when only one word ( like "interest" ) appears, but it refers back to two things
Look at this sentence:
> *Their confidence increases, **as do their interest** in communicating. *
Even though "interest" looks singular, the writer uses **do** because the sentence really means:
*Their confidence increases, **and their interest** in communicating also increases. *
The auxiliary **do** refers to **both confidence and interest** – two separate things.
However, many native speakers would find this unnatural. The more common and correct version would be:
> *Their confidence and interest increase, **as does their motivation**. *
> or
> *Their confidence increases, **as does their interest** in communicating. * ( if you treat interest as the only new subject )
In formal English, if you have only one singular noun after "as", you should use **does**. Using **do** with a singular noun is generally considered a mistake unless the context clearly implies a plural subject.
- - -
### Simple decision chart
| After "as" you see. . . | Use |
| - - - - - - - - - - - - - - - - - - - - - - | - - - - - - |
| one singular noun ( e. g. , *his ability, their motivation, my interest* ) | **does** |
| two or more nouns connected by "and" | **do** |
| a plural noun ( e. g. , *their skills, the students, many reasons* ) | **do** |
- - -
### Examples side by side
| Correct with "does" | Correct with "do" |
| - - - - - - - - - - - - - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
| *Her writing improves, **as does her grammar**. * | *Her writing improves, **as do her grammar and punctuation**. * |
| *Their confidence grows, **as does their interest**. * | *Their confidence and interest grow, **as do their skills**. * |
| *My reading speed increases, **as does my vocabulary**. * | *My reading speed increases, **as do my vocabulary and comprehension**. * |
- - -
### Final advice for your exam
If you see a sentence like:
*"Their confidence increases, as _____ their interest in communicating. . . "*
- If the sentence has already mentioned only "confidence" and now adds "interest" as a new singular item, most standard grammar books would choose **as does** ( because "interest" is singular ) .
- However, some test makers may argue that "confidence" and "interest" are two separate things, so the auxiliary should be plural: **as do**.
To avoid confusion, remember this:
**If you can replace "as do/does" with "and . . . also" and the subject after it is singular, use "does". If the subject after it is plural or compound, use "do". **
When in doubt, choose **does** for a single singular noun – that is the safest and most widely accepted rule.