The monogamist would say, “I’d like to introduce my wife, Mary.” Because the monogamist has only one wife, the name Mary is extra, descriptive (nonrestrictive) information and therefore is set apart from the rest of the sentence with a comma (or commas, if the sentence continued after the name). The bigamist, however, needs to distinguish between his wives, so the name Mary is essential (nonrestrictive) and is not set off. Similarly, someone with one son would say, “My son, Jim, plays Little League.” A person with two or more sons would say, “My son Jim plays Little League.”