Question

Can you explain the differences in these terms, and the function they serve when writing an essay?

thesis and thesis statement
central reasoning and central relationship


The <b>thesis</b> is your central idea, your main idea, the point you are trying to prove in your paper. The <b>thesis statement</b> is the one sentence in the paper in which you state this idea.
http://grammar.ccc.commnet.edu/grammar/composition/thesis.htm

<b>Central reasoning</b> -- I haven't heard that term before, but it seems as if it would include the primary reasons (evidence, examples, data, etc.) you are using to prove your thesis.

<b>Central relationship</b> -- I haven't heard of that one before either.

Here are some grammar/writing websites where you can try to look up various terms:
http://grammar.ccc.commnet.edu/grammar/index2.htm
and
http://leo.stcloudstate.edu/catalogue.html
and
http://nutsandbolts.washcoll.edu/
(Use the column at the left as the table of contents.)

=)