Thesis (plural: pronounced THEES-eez): The point that an essay is trying to prove. Everything in a persuasive essay relates to the thesis, either as evidence, explanation, elaboration or rebuttal of alternative claims. Just as all the parts of your body are connected to the spine, and without the spine your body could not stand, so too in your essay all parts must be connected to the thesis, and without the thesis the essay cannot stand.
Parts that are not connected must be revised so that they do connect, or else eliminated.
In order to get an adversary to listen to an opposing idea, it is important to treat him or her with respect.
This means being willing to see worth in that conflicting viewpoint.
So my example above is not a valid thesis, because everybody knows what color the sky is.
An arguable thesis might be, for example, The sky only became blue about 1 billion years ago, when the composition of the atmosphere changed to produce the specific refraction of sunlight that makes it look blue. (I have no idea if this is true or not, by the wayits just an example.) This statement is not obvious, and it would require evidence about the nature of the atmosphere a billion years ago, and explanations of why that evidence is reliable, in order to be proved.
Therefore, In some cases a descriptive thesis may strongly imply a prescriptive argument as well (as in most of the examples above).
However, note that one can agree or disagree with the descriptive thesis regardless of how one feels about the moral question.
A descriptive thesis makes a claim about how things your illness.) You can agree with someone about how things are even if you dont share their values.
But you cant agree on how things should be unless you share at least one value.