Final answer:
The statement primarily appeals to ethos by leveraging the authority of Harvard professors to persuade the audience on the importance of learning a second language.
Step-by-step explanation:
The statement “The research - conducted by professors at Harvard University -- suggests that you should learn a second language.” primarily appeals to ethos. Ethos is the credibility or ethical appeal which involves persuasion by the character of the author. When the statement mentions that the research is conducted by professors at Harvard University, it is leveraging the credibility and authority of the institution and its scholars to persuade the audience. In other words, it implies that because the research is affiliated with a reputable institution, it should be taken seriously, and the advice it offers should be considered.
On the other hand, logos refers to the logical appeal, where reasoning and evidence are used to persuade the audience. If the statement provided data, statistics, or empirical evidence supporting the benefits of learning a second language, it would be an appeal to logos. Similarly, pathos is an emotional appeal, which aims to persuade by evoking emotions in the audience. Finally, kairos refers to the timeliness of the argument, emphasizing the right moment in time to present an argument or appeal for maximum effect.