Hi Lenka, To clarify the point Bob makes I’d give this example. In appositions, the indefinite article implies the listener is not familiar with the modified object (person), while the definite article implies he is or he should (is supposed to) be. Leo Tolstoy, the great Russian writer, …- Everybody knows Tolstoy and the listener is supposed to know him. Leo Tolstoy, a great Russian writer,…. – It may sound insulting, the speaker presumes the listener is an ignoramus. In some cases, by adding the definite article we exalt the object, give it a higher rank in terms of fame or importance – thus, .