Syntax and diction are more than terms you had to define for your high school English class; they are the foundations of effective communication. Whether you need to write a professional letter or give a short speech presenting your ideas on a subject, paying attention to your syntax and diction will make a huge difference in whether your message comes across as clear or vague to an audience, and if they trust your credibility.
Diction refers to the choice in words you use to describe your thoughts and ideas. Choosing the best speech and writing for different contexts requires using different language for different situations. The effect of diction in changing contexts can make all the difference in how an audience perceives you, whether you seem credible, interesting, precise, or none of the above. A lawyer speaking to a judge in court requires polite, formal diction.
Syntax refers to the sentence structure of your language. The way you craft the phrases that make up your sentences influences an audience's reception of your communication. Strategic communicators outline their ideas, and group information into a series of points that help them direct audience members to significant parts of their speech. The effect is that audience members hear a series of points the speaker makes, remembers them and is then able to evaluate the information in their own time.
Artful communicators shape their syntax and diction to make a dramatic impact on their listeners, using the rapport they gain with an audience to increase their persuastion. Audience members perceive strong, effective communicators as more credible. A speaker who delivers a speech using vague language and a rambling style may confuse an audience. This tends to cause audience members to feel frustration with the speaker for not clearly communicating their message and casts doubts on the expert's level of professionalism.
The overall message you convey results from your diction and syntax. Tones range from authoritative to meek, friendly, remote, inflammatory, formal or informal. A communicator using combative language to persuade an audience may turn an audience away, losing their rapport with them and closing them off to receiving the information the speaker wishes to convey. Different audiences require different tones of communication. Speaking to high schoolers may require a friendly, informal tone, whereas a nurse speaking to patient may require to use a combination of both gentle and firm language.