The example given according to Aristotle, Averroes and Avecina, was the discussion of propositions and classification of these propositions, was ""Every man is just" and its counter two propositions 1) the negation by saying "No man is just" as opposites like white and black, good and evil, and 2) "Every man is unjust" which is contrary to the basic statement. The significance of the contrary proposition according to Averroes was demonstrated by the example which is not contrary proposition, is "Death is bad" as opposed to "life is good" because both are true propositions, therefore, contrary propositions is One must be true first, and the other false. What we believe, therefore, is the most contrary while others have general meaning of the contrary.
To give more concrete example, in the argument of the uttering [the speech] and its mental perception in tems of negation or contrary, we have to ask: Is belief in the contrary of a given proposition or belief in its negation stronger or weaker than the original statement. Or to apply it to belief: Is belief in the contrary of a given proposition or BELIEF in its negation is [greater] stronger. And is there stronger than both propositions?
In the Arabic language which colors Islamic belief of "Tawhid" or "Oneness" of God. The Qur'anic statement by uttering " La Ilaha Illa Allah" Which means there is no god except One God, the statement demonstrates new type of proposition which is "negation of the negation" This means that this type is stronger than both the negation and the contrary assumptions together. Logically then, philosophers reach to the natural conclusion that God exists at the beginning and end of propositions.
Note: I owe a great debt to for those who discussed previous the three terms thoroughly in there commentaries and writings, namely, Aristotle, Averroes, Avecina, al-Ghazali, and Butterworth. In addition to summeries of Moses Maimonide and Thomas Aquinas. The proverb saying "we stand on the shoulders of the Great philosophers", may be applied here.