Analyzing the following expressions:
The expressions above are oxymorons, meaning that they put together words whose meaning are contrasting. We would assume that, if something or someone is pretty, they cannot be ugly; if something is true, it cannot be a lie.
That, however, is not the real purpose of this rhetorical device. The apparent contradiction mentioned above is precisely that: apparent. It does make sense in context because the first word serves as an intensifier of the second word.
We can observe that in the following examples:
- The bruise on his leg after the accident was pretty ugly.
- I can't believe she said that to you! Those are true lies.
In both instances, the first words of the oxymoron are intensifying the second one. The cut wasn't merely ugly, it was very ugly. "Pretty" does not keep its original meaning in this context.
The same happens with the word "true". The lies told were extremely obvious. "True" does not keep its original meaning either.