McGraw-Hill Public Speaking

Selecting a topic




Developing and refining your central idea and purpose

Once you select a topic that meets the assignment, situation, and audience, it needs to be refined into a central idea.

Begin with your general purpose

In assessing your speaking situation, you should have reached some conclusions about the type and purpose of your speech. If not, now is the time to ask yourself whether your speech is intended to inform, persuade or entertain. For classroom assignments your teacher will let you know. If you need to figure out your general purpose refer to assessing your speaking situation.

Refine it into a specific purpose

Your specific purpose statement combines your topic with your general purpose. It combines the two in a single infinitive statement. Use the word "to" to begin your statement.. Record each item individually, as shown in the example below.

Topic: Car brakes

Purpose: To inform.

Specific purpose: To inform my audience about car brakes.

The specific purpose should state your purpose precisely. The specific purpose above begins with an infinitive and is written as a complete statement. However, it provides little detail about the aspect of car brakes you will be speaking about.

Specific purpose: To inform my audience about braking methods for cars with and without anti-locking brakes.

Now the specific purpose statement has a clear and focused purpose. It will be easier to state your central idea.

State your central idea

Your central idea should summarize the main points of your speech. It states the message you want your audience to remember when your speech is done.

Central idea: In an emergency situation, the hard braking method used to stop cars with anti-lock breaks can lock up traditional brakes on older rear-wheel and front-wheel drive cars.

The central idea teaches us several things: (1) there are two types of brakes in cars (2) older cars have traditional brakes (3) different methods are required for safe braking depending on the type of brakes a car has.

The central idea does not simply restate the specific purpose. The central idea reveals the content of your speech. You can formulate your specific purpose shortly after selecting your topic. However, you should allow your research to lead you toward a central idea rather than approach the speech with preconceived notions.

Both your specific purpose and your central idea will be more effective if you:

  • express each as a single, complete sentence
  • avoid stating the sentence as a question
  • use clear language
  • avoid vague or general statements


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