A letter written to a wife can be:
* A primary source: If you are researching the life of the wife or the relationship between the husband and wife, the letter itself is a direct account of their experience. It's a firsthand document.
* A secondary source: If you are using the letter to learn about a historical event or social trend, the letter is a secondary source. It's someone's interpretation of events, rather than a direct account of the events themselves.
Example:
* Primary Source: You're researching the life of Mary Smith. Her husband John wrote her a letter in 1850 detailing his struggles finding work. This letter is a primary source because it directly provides insight into Mary's life and John's experiences.
* Secondary Source: You're researching the impact of the Industrial Revolution on families. You find a letter from a husband to his wife in 1850 discussing the challenges of finding work. This letter is a secondary source because it indirectly provides information about the Industrial Revolution through the lens of the husband's personal experience.
In short, the source classification depends on what you're using the letter to learn about.