Characteristic - विरोधः सोऽविरोधेऽपि विरुद्धत्वेन यद् वचः।
(Actually) Where there is no contradiction but where the words showing contradiction are used the figure of speech is (विरोधः) i.e. Paradox.
For example
या निशा सर्वभूतानां तस्यां जागर्ति संयमी ।
यस्यां जाग्रति भूतानि सा निशा पश्यतो मुनेः ॥
(Meaing of the Shloka: That period of the day which is the time for sleeping for common men is the time for keeping awake for Sanyasins and when common people keep awake the Sanyasins sleep.)
It is very well-known that the right time is the time for common animals to sleep. Still however, contradiction is shown by pointing out that time is the time for Sanyasins to keep awake. In the same way, contradiction is shown by nothing that the period of time when common animals keep awake eat and move that Sanyasin sleep. So here the figure of speech is said to be paradox.
(Special note: right means retirement and 'Jagaran' i.e. wakefulness/sleeplessness means activity. When common people remain angaged in activities of comfort and enjoyment the Sanyasins rest, they remain retired not doing any activity. Thus the contradicting situation is described here and that creates wonder.)