Thesis Statement

Overview
The thesis, or claim, is the guiding idea of an argument.  It is, in short, the claim that you will be supporting with reasoning and possibly research.

What a Thesis Should Do
A thesis will generally accomplish several things:

• It asserts a specific position about the topic.
• It conveys the reason for asserting and defending that position (in other words, why are you writing this?)
• It sometimes provides a concise preview of the reasons that support your position.

The classic thesis statement is "X is Y because A, B, and C."

• "X is Y" is the claim being made.
• "A, B, and C" would be the supports of that claim.

Now, that may be the classic model, but you'll find very few writing assignments or claims lend themselves to something quite that neat. Instead, you're like to see things like:

• Although X is sometimes Y, in the majority of circumstances, it is Z. Given A, B, and C, the concerns about Z far outweigh the benefits of Y.
• Although X is usually Y, the instances in which X is Z are signficant enough to cause concern is A, B, and C.

Okay, so these abstracts don't make much sense. Let's try something more concrete. 

What I want to argue is that the portrayal of women in slasher films, which has often been attacked as sexist, is actually positive in many ways. Now, I can't ignore that there are problematic aspects, so I might want to work that into the thesis. Also, I want to give my readers some idea of how I'm going to support my case.

Sample Thesis: Although certain Hollywood stereotypes are still present, the portrayal of women in slasher films is far more positive than it's been given credit for. The significant number of female protagonists, the strength and intelligence of those protagonists, and their tendency to have interests outside of boys and dating, all contribute to a positive portrayal of young women.

This thesis can then be broken down into parts: concession (Although certain Hollywood stereotypes are still present), claim (the portrayal of women in slasher films is far more positive than it's been given credit for.), and support ( The significant number of female protagonists, the strength and intelligence of those protagonists, and their tendency to have interests outside of boys and dating, all contribute to a positive portrayal of young women.).

What a Thesis Should Not Do
While a thesis should indicate what you are going to be writing about, it should not include statements like "I am going to write about" or "I will argue that." On rare occasions, it might be appropriate, but very seldom.