"What things there are to write if one could only write them! My mind is full of gleaming thoughts; gay moods and mysterious, moth-like meditations hover in my imagination, fanning their painted wings. They would make my fortune if I could catch them; but always the rarest, those freaked with azure and the deepest crimson, flutter away beyond my reach.
"The childish and ever-baffled chase of these filmy nothings often seems, for one of sober years in a sad world, a trifling occupation. But have I not read of the great Kings of Persia who used to ride out to hawk for butterflies, nor deemed this pastime beneath their royal dignity?"
(Logan Pearsall Smith, More Trivia , 1921)
The function of an argumentative essay is to show that your assertion (opinion, theory, hypothesis) about some phenomenon or phenomena is correct or more truthful than others'. The art of argumentation is not an easy skill to acquire. Many people might think that if one simply has an opinion, one can argue it successfully, and these folks are always surprised when others don't agree with them because their logic seems so correct. Argumentative writing is the act of forming reasons, making inductions, drawing conclusions, and applying them to the case in discussion; the operation of inferring propositions, not known or admitted as true, from facts or principles known, admitted, or proved to be true. It clearly explains the process of your reasoning from the known or assumed to the unknown. Without doing this you do not have an argument, you have only an assertion, an essay that is just your unsubstantiated opinion.