It �s very common to hear students say "I have a doubt" to mean "I have a question". These students are Spanish speakers and therefore are translating the phrase "Tengo una duda", which is very common in Spanish. Saying just "I have a doubt" is unusual in English when someone has a question.
Saying "I have a doubt about �something � is okay and good.
There are other correct uses of the word "doubt":
(be) in doubt about sth (= feel unsure): �Is anyone I doubt about what they �re supposed to be doing? � �If you �re in any doubt about your child �s safety, talk to your doctor.
However, it is more common to say "I �m not sure" or "I �m uncertain" about something.
without doubt = �I firmly believe this to be true �; �He"fs without doubt one
of the greatest composers the world has ever IInown. �
no doubt = �I expect � or �I suppose �: �No doubt you could do with a drink. �
�They will no doubt be writing to us again.
there is no doubt that (NOT it is ... ): �There is no doubt that the number of casualties would have escalated had it not been for UN intervention. �
There is no doubt that is usually used in formal styles when you want to persuade someone that what you are saying is true: �There is no doubt that the present government has lost a great deal of support. �
This phrase is sometimes used when a �lighter � expression (e.g. of
course, obviously, clearly, certainly, needless to say) or nothing at all
would be more natural.
When doubt is used to express certainty or near certainty, it is usually
followed by a that-clause: �There �s no doubt that he �s innocent. � �I �ve no
doubt that he �s innocent. � �I �m in little doubt that he �s innocent. � �I don �t
doubt that he �s innocent. � In this meaning, doubt is used with a negative
word, e.g. not/nollittle/not much.
When doubt means �think that something is unlikely �, it is usually followed by if/whether: �I doubt whether he �s innocent. � (= I think that he is probably guilty) �She doubts whether she �ll be able to come on
Sunday. �
Note that some people may also say �I doubt that he �s innocent �, but
careful users regard this as incorrect.
have (your) doubts about (doing) sth = feel unsure whether something
is true or the right thing to do: �We have our doubts about sending Kevin
to a boarding school. � �Any doubts she �d had about marrying him soon
disappeared. �
