Perhaps you could clarify what you mean by "borders of themes" and provide one or two examples from different areas in which it applies.
Thanks,
John

well some themes are often used for example religios themes. but for example loudspeakers and used cars are not used.

Ow... anyone have an aspirin?

Perhaps a tad more clarification?

Perhaps it is that certain "themes" or ideas more readily capture the artistic imagination. One thinks of the Madonna and Child, Christ on the Cross, seascapes (particularly storms), nudes, battle scenes, heroic moments, and landscapes (mountains).
But this does not mean that all artistic creations are confined to expressing such themes---Andy Worhal's soup cans, Bosch's haunting scenes, or many of the great photographs that picture common objects.