What is a thesis? And what is a (appropriate) topic sentence ?

A thesis statement is (often) a single sentence that explains the basic idea that will be developed in the paper. It declares the main purpose of the entire paper.

Below is something that is handed out to our students before they write a paper. I am not sure where it originally came from, but it is in every room of our school.

A good thesis statement should
Fulfill the assignment.
Assert one main idea
Be clearly stated in specific terms
Say what it means.
State an attitude or opinion.

A bad thesis statement
Insult the reader.
Use general statements.
Be a figure of speech.
Consist of facts or data
Start with, "My purpose is…"
"I intend to show that…"
"In my opinion…"
"I feel…"