Chapter XIII The Articles
§ 547. The rule of most practical importance about the articles is the rule that determines when the article shall be repeated as often as there is a fresh substantive, and when it shall not.
When two or more substantives following each other denote the same object, the article precedes the first only. We say the secretary and treasurer (or, a secretary and treasurer), when the two offices are held by one person.
When two or more substantives following each other denote different objects, the article is repeated, and precedes each. We say the (or a) secretary and the (or a) treasurer, when the two offices are held by different persons.
This rule is much neglected.