Communication, both spoken and written, is always addressed to an audience, a set of listeners or readers you are intending to convey information to or have some effect upon. Public speaking differs from written communication in that the audience is present, gathered for some occasion. That occasion has norms and expectations that a speaker must recognize. Finally, a public speaker has some purpose, something they are trying to accomplish or set in motion. Good public speaking always accounts for these three components.
Audience
Speakers communicate differently to different audiences. To take a simple example, people tell their grandmothers about their new “significant other” in a different way than they tell their best friend. Similarly, people speak about trees differently with their high school biology teacher than they do with their younger siblings; and speakers often need to make arguments about public policy differently to Republicans than to Democrats. Two main questions guide audience adaptation in a speaking situation: Who are they? What qualities about them are relevant?
Who are they?
Distinguishing general from specific audiences is useful. A general audience is everyone who will hear the speech or read the paper. A specific audience, on the other hand, is that subset of the general audience who the speaker particularly wants to reach, or to reach in a different way than the rest of the group. In an audience with varying degrees of knowledge on a subject, for instance, a speaker might want to pitch their comments primarily to non-experts (while at the same time not saying anything that a specialist would find objectionable). In the classroom, students may be speaking to the entire group but making a special effort to address the professor's expectations.
What qualities about them are relevant?
Audiences vary in values, knowledge, style of communication, and intellectual capacity—among other qualities. Depending on the topic and purpose, effectiveness could be influenced by whether the audience is young or old, rich or poor, female or male, highly religious or less believing, college graduates or high school dropouts, ethnic minorities or majorities. In addition, audiences carry different expectations to a speaking occasion: some want to be there, others do not; some want to be entertained, others are looking to be informed; some are open to being persuaded while others are unlikely to change their minds anytime soon; some expect a highly polished presentation with sophisticated visual aids while others are looking for less formal comments. All of these expectations help shape a speaking situation.
Occasion
Unlike much written communication, a public speaking situation occurs at a specific time and place. With regard to time, the speech can be affected by events that have very recently occurred (e.g. the morning's news may be fresh in your audience's mind); by the time of day (8:00 A.M. lectures are different than 10:00 A.M. lectures); and by the fact that it comes after or before other speeches. Place matters too--different-sized rooms make a difference for visual aides and intimacy.
There is also a reason that the speech is happening, the occasion for which the audience has gathered. Are you speaking at a wedding or a funeral? An academic lecture series or a public meeting of concerned citizens? A mandatory assignment for freshman communication students? Each of these occasions has different norms for speaking, calling for speakers to operate in different modes--from formal to informal, from light to heavy, humorous to serious, conversational to highly practiced.
Purpose
Speakers hope to accomplish general and specific purposes when they communicate. For most speaking in college and beyond, there are two general purposes: to inform or to persuade. The line between informing and persuading is not absolute, and many speeches will do some of both. Nonetheless, they are useful guides for speakers.
When a speaker seeks to inform, they want the audience to leave the speech knowing more than they knew beforehand. Speakers may want to explain an idea or process, share new information, or show how to do something.
When a speaker aims to persuade an audience, they want them to adopt a new position or belief, to change their minds, or to be moved to action. Persuasion calls a speaker to advocate one position among others that are possible and be willing to defend it against challenges.
In addition to a general purpose and speaker typically has a range of more specific goals for their speech. They may want to get a few laughs, to build upon a classmate's speech, to reach a selected group of listeners, to show themselves to be competent to potential employers, or to create controversy! A successful speech requires a clear sense of general and specific purpose to guide how selection and presentation of ideas and words.