I am studying english and I saw this rule: The book is on the table/ but The book is on a little table
The flowers are in the vase / The flowers are in a beautiful vase.
The rule says that one can use any noun, adjective and preposition here, but when you define the noun with the adjective in such structures with the preposition, you should use the indefinite article.
So we have the same situation here (ex.:The flowers are in the vase / The flowers are in a beautiful vase.), but if we define the noun "vase" we should use the indefinite article. Is this true? Does this rule always work? I would appreciate it if somebody clarify this for me.