Normally, the function of poetry or rhetoric, according to writers on poetics and literary criticism, is to represent good things as good and bad things as bad. However, already in ancient Greece poets and orators delighted in perversely describing good or beautiful things as bad or ugly, and "vice versa". The same is found in Arabic literature, where this ability was sometimes called the hallmark of excellence in a poet. Going against received opinion ("paradoxos"), which has been termed "taghayur" in Arabic, is a favorite practice of several writers and poets, including al-Jahiz and ibn-al-Rumi. Another term for this phenomenon is "tahsin al-qabih wa-taqbih al-hasan", which is also the title of one of al-Tha'alibi's many anthologies, here discussed in more detail. In some cases the "paradox" is put to subversive purposes;more commonly, it serves to show the poet's skill or wit.