1

May I ask which one is correct "a spouse of", or "the spouse of". Example: Dana is a/the spouse of Peter. Thanks.

2

Basically, the difference between the and a/an is one of specificity and shared knowledge.

the indicates that this is knowledge that is shared between you, the speaker, and the listener/reader. a indicates that you might not know about this instance of the thing.

Here's an example of it from a WDSU news story (my emphasis):

Police are looking for an armed man in connection with an attempted murder in New Orleans East.

The incident happened in the 6000 block of East Hermes Street about noon Wednesday.

In the above excerpt, an is used to introduce something that you don't know about, after which the is used to refer back to it (anaphoric reference).

In your example, there is a difference in meaning between the two:

  • Dana is the spouse of Peter
    Without anything before it, we draw on shared cultural knowledge (homophora) to infer the meaning. In many Western societies where Christian religions have been dominant, it is understood that relationships are monogamous unless otherwise stated - that is, having one partner/spouse is the unmarked relationship.
    Also, because of this knowledge, using the is the less marked way of phrasing that (although saying Dana is Peter's spouse is even less marked)
  • Dana is a spouse of Peter
    Conversely, by using a, the more marked form of this clause, you are signalling that there is something unusual - ceteris paribus (all other things being equal), it would signal that Peter has more than one spouse.

Possibly related:

“the” vs. “a/an” + clauses

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  • I found your answer really interesting but was wondering if you know why even family relationships that aren't understood to be one-to-one are also generally identified with 'the'? i.e. 'Sarah is an employee of Mark's' vs 'Sarah is the daughter of Mark'? – jam Jun 19 '14 at 12:15
  • @jam these are probably bad examples; it is very unidiomatic to say "X is the Y of Z", it's much more natural to say "X is Z's Y" - that is, with your examples, "Sarah is Mark's employee", "Sarah is Mark's daughter". This makes it extremely difficult for me to decide whether "Sarah is the daughter of Mark" or "Sarah is a daughter of Mark" is more natural. I would expect "Sarah is the daughter of Mark" would be used if the relationship, or number of children, was in question - "Does Mark have twin daughters?" "No, Sarah is the daughter of Mark." or "Yes, Sarah is a daughter of Mark." – jimsug Jun 19 '14 at 12:20
  • Similarly, with employees, you could only really use "Sarah is the employee of Mark" in response to a similar question, whereas "Sarah is an employee of Mark's" could be used in response to a question like "Is Sarah one of Peter's employees?" "No, Sarah is an employee of Mark's". But as I said, these are all highly marked, and I would expect in unmarked, natural dialogue, that speakers would use 's to show possession and this kind of relationship. – jimsug Jun 19 '14 at 12:23
  • @jimsung thanks for your answer. The example which made me ask is you sometimes get '<x> is the daughter of <more famous person y>' in print, but on reflection I guess that does fit your initial explanation - X is clearly the daughter of someone, so we can use 'the' because there is knowledge. I agree it would be weird the other way round in an unprompted statement. – jam Jun 19 '14 at 13:11