What are three communication contexts?

I'm not sure what you mean by this, but since you are asking under the category of public speaking I'm assuming you're referring to ethos, logos, and pathos.

Ethos refers to credibility. - How a speaker presents him/herself and is perceived by the audience falls under ethos. If a speaker is dressed nicely, speaks proper English, and uses appropriate nonverbal elements, the speaker may appeal to ethos very well. In some cases, ethos alone may make a speaker seem smart, regardless of how well the speaker uses logos.

Logos refers to logic. - Ethics aside, any information presented as fact by a speaker falls under logos.

Pathos refers to emotion. - Those sad dog commercials that play really depressing music and shows images of abused animals rely on pathos. If the audience feels sad/bad for the animals after watching one of those commercials, then the commercial appealed to pathos well.