The key words of each definition are an indication of their differences:
- Speech: communication, conversation, expression, audience
- Rant: anger, violence, extravagance, bombastic, loud
While both are forms of communication that may or may not be prepared in advance and are delivered by a speaker, they are clearly not the same in their characteristics nor in their intent.
There are three primary differences between a rant and a speech. The first is delivery. A rant is generally delivered with violence whereas a speech is not, though a speech may be delivered with genuine passion. The second is purpose (motivation). A rant is louder and more strident than speeches will be because the goal of a rant is to express a violent or angry position to the audience. The third is content. The content of a rant is always unmitigated biased opinion because the speaker wants to verbally assault his audience, sometimes to instigate action, sometimes only to lambaste targeted individuals or society in general. The content of a speech might be intended persuade audiences to action or new opinions but it also might inform or entertain.
Clearly there is a distinct line between these two forms of expression, and sometimes what begins as a speech can, through excessive, extravagant emotion and lack of psychological control, end up as a rant. For example, when the lines of decency or propriety have been crossed for the audience, the speech has become a rant as happens often with comedians who go just a bit too far for the audience to tolerate; when this happens, it later appears in the news and is called a rant.
In common practice, a speech is a prepared presentation which delivers information to an audience for a specific purpose; a rant is a loud, angry tirade designed to express violent emotion that often incites reactionary emotion in the audience. To illustrate the significance of the differences, in the closing argument of a court case, lawyers do well to deliver speeches rather than excessive, antagonistic rants.