Generally, using the author's last name is the safer and more formal approach. This is especially true for:
* Academic essays: Formal academic writing usually prioritizes formality and avoids overly familiar language. Using the last name maintains a respectful and professional tone.
* Essays for unfamiliar audiences: If you don't know your audience's preferences, using the last name is the best way to avoid seeming presumptuous or unprofessional.
Using the first name *can* be appropriate in certain circumstances:
* Informal essays: In less formal settings, such as a blog post or personal essay, using the first name might be acceptable, especially if the tone of your writing is already informal.
* Essays focusing on the author's personality or life: If your essay delves deeply into the author's life and personality, using their first name might make the writing feel more personal and engaging. However, even then, it's a judgment call. You might initially use the last name and transition to the first name later in the essay to signal a shift in tone.
* If the author themselves prefers it: Some authors actively encourage readers to use their first name. If you have evidence of this (e.g., they state it on their website or in an interview), then it's perfectly acceptable.
In short: When in doubt, use the last name. It's always better to err on the side of formality, especially in academic or professional contexts. Consider your audience, the tone of your essay, and any information available about the author's preference before making a decision.