Final answer:
A letter from Thomas Jefferson to James Madison is a primary source because it is an original document from the period being studied, offering a first-hand account of events, making it direct evidence in research. Option number a is correct.
Step-by-step explanation:
The letter from Thomas Jefferson to James Madison is considered a primary source. In historical research, a primary source is an original document or record that was created at the time under study. It is a direct, first-hand account of an event, a person, or an idea. Examples of primary sources include government documents like the United States Constitution, diary entries, letters, photographs, and interviews.
When evaluating historical documents, it's important to recognize that primary sources provide direct evidence about the subject of inquiry. They are highly valuable in research because they offer the closest perspective to the events being studied without the filter of interpretation that characterizes secondary sources. Therefore, a letter written by Thomas Jefferson to James Madison, being a direct communication between two historical figures from the time period being studied, serves as a primary source for researchers looking into that area of history.
Secondary sources, on the other hand, analyze, interpret, or review information from primary sources. They often provide perspective and context but are one step removed from the original event or period. An example of a secondary source would be a modern biography or a historical analysis of Jefferson's letter.