وَإِنْ كَانَا مَعْرِفَتَيْنِ، فَاجْعَلْ أَيَّهُمَا شِئْتَ مُبْتَدَأً، وَالْآخَرَ خَبَرًا.
Translation: If both nouns are definite, either may be taken as mubtadaʾ and the other as khabar.
The source permits both analytical orientations in this basic category. In actual usage, intended predication, discourse context and emphasis help determine which element is the topic and which is asserted about it.