Use sound premises in developing your thesis. A premise is a statement that expresses your arguments or that presents evidence. Premises should be relevant to the theme of your thesis and should be true. They should also provide good support for your conclusion. There should be no idle "fillers" in your thesis that detract from the main message or the goal that you are trying to lead the reader to. Check to ensure that you have addressed the most important aspects that relate to your thesis. Do not making sweeping claims that you are unable to support.
Avoid hasty generalizations. A whole group should not be judged based on the actions of a few in that group. For example, you might have had two "mean" math teachers in high school. You conclude that "all high school math teachers are mean." In this case, your sampling is too small to make generalizations about all high school math teachers. Another way of avoiding hasty generalizations is to not use stereotypes such as "people from such and such country are dirty," or "librarians are quiet and intelligent." Using a few examples to prove the point is not enough to support generalizations about groups of people. Premises should be based on factual evidence that is scientifically investigated, such as considering documented case studies or controlled clinical studies. Conclusions that are not dogmatic but modest, are more easily digested by the reader and easier to support.
Examine your thesis paper for post hoc fallacies. (Post hoc fallacy is also referred to as "false cause.") Post hoc, in Latin, means, "after this." An example of a post hoc fallacy might be, "After the death of Theodore Roosevelt, Hitler rose to power; therefore, the death of President Roosevelt contributed to Hitler's ascent." In order to add any legitimacy to this argument, the writer would have to establish a causal link between Roosevelt's death and Hitler's rise to power. Because such a link would be very difficult to establish, it might be considered a post hoc fallacy. It would be best to use only examples that demonstrate a more direct cause-and-effect relationship.
Separate your premises from your conclusion. The Writing Center of the University of North Carolina at Chapel Hill encourages students to look at the premises and "ask yourself what conclusion an objective person would reach after reading them." Think about what type of evidence would be necessary to reach the conclusion of your thesis and determine if your premises provide enough evidence. If not, you might be missing the point and you may need to narrow or modify your thesis, or provide more evidence to support it. There are a number of other types of fallacies that you can research and learn to avoid in developing a logical and sound thesis.