Deliberate oxymorons
Often a writer will use an oxymoron in order to deliberately call attention to a contradiction. Richard Feynman, for example, in his lectures on physics, spends a chapter discussing "dry water" [2]. Clearly, he could have used a different phrase, such as perhaps "hydrodynamics of fluids in the limiting case of viscosity approaching zero," but the deliberate contradiction of the phrase "dry water" both adds humor to his otherwise-dry analysis, and also emphasizes the fact that the substance he is discussing is theoretical and not real.
Some examples of deliberate oxymorons include:
Deafening silence
Sweet sorrow
Forward retreat
Accidentally on Purpose[3]
Oxymorons are most tellingly employed in injecting a sense of ironic, ostensibly unintended, humor. The effect is to confront the reader or the listener with a sense of ludicrousness so as to render the whole sentence and the idea absurd and funny. It should be remembered that this is a purely subjective line of thinking and presupposes that the reader or listener is already familiar with the intended humor. Examples of such thought-provoking oxymorons include:
Orphans of the Living - children in the foster-parent system.
"Poet in residence in absentia" - a title granted to a poet, at his own request, by a university.