Is it okay to use their in this case:

If one is driving a smelly car, it is most likely that their hygiene is horrible.

Well, their is definitely plural, and one is singular, so I think it should match, but just using "his" or "her" sounds partial, and using "his or her" is, in my opinion, too redundant.

So is it fine to use their like this?

  • 1
    Singular they.
    – The Photon
    Jul 6, 2016 at 19:17
  • 1
    But if you're formal (and British) enough to use "one" as a pronoun in the first clause, you might as well use "one's" in the main clause.
    – The Photon
    Jul 6, 2016 at 19:18

3 Answers 3


If one is driving a smelly car, it is most likely that their hygiene is horrible.

I would suggest two changes for this sentence.

If you use one, it means that you are talking about people in general, including yourself. I don't think that I would want to include myself in a sentence like this, so someone or somebody are better words to use.

Note that, if you use someone, it is OK to use the gender-neutral their (the genitive form of singular-they). If you want to stick with one, you should be consistent and use one's instead of their.

is driving is present continuous: used with if, the second clause specifies only what happens only during the time that the person is driving,

If you are driving, you should wear your safety belt.

So present continuous in your sentence is likely to be interpreted as

at any time when somebody is driving a smelly car, their personal hygiene is poor (but might be OK when they are not driving).

It would be better to use present simple drives to refer to a habitual action. Used with if the second clause refers to the person's permanent state. This would be interpreted as

If somebody is in the habit of driving a smelly car, their personal hygiene is likely to be poor at all times.


Native speaker here. The sentence seems awkward, but I'm not sure how to correct it because I don't know if "one" and "their" are meant to refer to the same person. Be careful with "one", because you cannot connect it through a conversation; it always introduces someone new.

If you intend "one" and "their" to refer to the same person, then perhaps something like this will work:

If you're driving a smelly car, then it's probably because your hygiene is horrible.

Using "you" here seems the natural choice.


That's fine since the plural, they/their, is used when gender is ambiguous.

  • 1
    It's not the "plural", though, because it can refer to just one person - it's called "singular they".
    – stangdon
    Jul 6, 2016 at 19:19
  • I think it's stylistically weak (arguably, appalling) to mix one's and their as in OP's example. At least one / you should be consistent - pair up one / one's or they / their (or even "generic" you / your). It's always going to look strange if you can't make up your mind which way to go. Jul 6, 2016 at 21:30
  • Oy, yes, it's the singular they but it's the plural form as it also takes the plural verb form.
    – DTRT
    Jul 7, 2016 at 18:03

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