Style of language

Barack Obama’s style of language in the “Audacity of Hope” speech is formal, which mirrors the seriousness of the context in which his message is delivered. 

When it comes to sentence structure, Obama uses sentences of various lengths. Short sentences, for example, draw attention to a particular idea: “Now let me be clear. We have real enemies in the world. These enemies must be found. They must be pursued and they must be defeated. John Kerry knows this”. In this example, the short sentences draw attention to the seriousness of the war in Iraq and to the fact that Americans need to be aware of the existence of enemies. 

Longer sentences are used when Obama touches upon more complex issues:

Tonight, if you feel the same energy I do, the same urgency I do, ...