Continuing your studies beyond a master's degree means proving to an admissions committee that you have the academic drive to complete a rigorous program and make a significant contribution to the field of your choice. When you request admission to a doctoral program, your letter should highlight your individual qualities, in particular your potential to conduct outstanding research. The letter should not focus on just your past academic achievements, but should outline your future research agenda as well.
Each university has a unique policy for doctoral program admissions; identify the appropriate committee, department, professor or other person to whom your letter should be addressed by consulting the admissions instructions. Use the correct title when addressing your letter to a professor or administrator; for example, write "Prof. Brown" instead of "Mr. Brown." Avoid generic salutations such as "Dear Sir or Madam" or "To whom it may concern," because they communicate a lack of effort to ascertain who is responsible for the admissions process.
Program of Study
When applying for a doctoral program, identify the school and department to which you are applying and the name of the person or persons whom you want to supervise your dissertation, if applicable. For example, if you are carrying out research about the United Nations Human Rights treaties with a law professor, your letter should explain, "This letter is my formal application for admission as a doctoral candidate in the faculty of law under the supervision of Prof. John Doe. The proposed subject of my dissertation will be: 'Core Human Rights Treaty of the United Nations.'"
You can set yourself apart from other applicants by demonstrating to the admissions officers that you are an experienced researcher. If you wrote a thesis for your master's degree, advise the committee of the topic and your grade; mention any other research that you have conducted, including research done in connection with fellowships or grants. Outline how your research will be carried out in future years; for example, you can tell the committee that your doctoral proposal is to conduct clinical trials of therapeutic devices on humans and that in the future, you hope your studies will add to the knowledge in the field by giving data that can be used to compare several therapeutic devices and their utility for certain patients.
Contribution to Knowledge
All doctoral research must contribute to the current knowledge in the field; that is, it may not merely duplicate or summarize what has already been done by other scholars. Your letter should demonstrate that you have already conducted a literature review in your field by reading the studies, reports, journal articles and books written about your topic. By mentioning what is already known, you can then explain what your research will add to that knowledge; for example, you can advise the admissions committee: "Chayes has examined supervisory mechanisms found in the World Trade Organization, and Keohane has studied the World Bank. My research will add to this knowledge by examining the same type of mechanisms at the International Monetary Fund."
Every doctoral candidate must first show that he has sufficient general knowledge in his field; for example, if you are a doctoral candidate in criminal law, you must show that you have a basic knowledge of the substantive and procedural laws in the field by passing oral and written examinations prescribed by the university. In your letter, you should point out courses that you have taken at the master's and bachelor's level that demonstrate your acquisition of knowledge in the field. This list of courses should also show that you have adequate background to conduct the doctoral research you have proposed in your application.