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