Informative speeches allow you to share new information to your audience and provide them with the benefit of your research. The purely informative atmosphere is best utilized when you speak to an audience who shares similar ideas or perspectives on an issue and your topic should reflect those shared perspectives. An example of an appropriate informative speech topic would be, "Results of cancer studies involving new medications." If your audience comprises people who are personally interested in cancer research or have a history of donating to cancer research, this informative speech would show them that new medicines may be available soon and that their money is well invested. Construct your topic with a factual reference to the information you want to cover.
An encouraging speech is best delivered to an audience who shares your ideals and whom you wish to motivate toward an action. Political speeches often fit in this category, with politicians hoping to convince a crowd to vote for them in an election. Topics for encouraging speeches are often simple, such as "Go vote" or motivational speeches such as "You can succeed." Encouraging speech topics should be short, positive and simple.
Persuasive speeches aim to change your audience's mind about a topic or to suggest a new course of action based on their current ideals. Your persuasive speech topic should be specific and suggest a plan. Persuasive topics may include "Begin your own neighborhood recycling program." Keep your topic understated, even if you are suggesting a radical change for your audience, to avoid alienating the audience with your topic.
Humorous speeches allow you to make light of real situations for a positive effect, such as during your best-man speech at a wedding or as part of a public address to a group. Your humorous topic should center on something familiar to your audience. For instance, a best-man speech may use a topic that makes light of the institution of marriage or relates a humorous story about the groom.