Final answer:
A doctoral student is pursuing a Doctorate (Ph.D.) degree, which is necessary for careers like a psychology professor at a 4-year college or an epidemiologist who conducts research.
Step-by-step explanation:
A doctoral student is someone who is pursuing a Doctorate (Ph.D.) degree. In fields like psychology, to become a professor at a 4-year college, one would typically need a Ph.D. degree. Similarly, many epidemiologists may have a Doctor of Medicine (MD) or a Ph.D. in an associated field, depending on their career path and the type of research or work they plan to engage in. It's also noteworthy that a Ph.D. can be earned in various disciplines, all of which fall under the broader category of 'philosophy' in the academic sense, but not specifically limited to the field of philosophy itself.
Different professions may require different levels of education, but for someone who wishes to work at a higher educational level, such as a professor or a researcher, a Ph.D. often becomes essential.