Abstract thought is not that hard, it involves, as stated above, the usage of symbolism and context. Symbols (including words and phrases) can have multiple meanings based on the context they are in. The letter "C" is often used to represent a constant in mathematics, but in chemistry it represents the element Carbon.
This can be extrapolated into common words and phrases. The phrase "I can afford that" can mean two different things, for example. If one is talking about getting a bottle of soda form a vending machine, the person is likely stating a matter of fact. However, if the person is talking about buying a private island, he is probably invoking a form of sarcasm: given his income status (unless he's Bill Gates), he likely isn't able to afford that. Sarcasm is in fact a form of abstract thought, attributing other meanings to certain phrases. (no joke, I really mean this).
But then again, this is coming from the guy who learned sarcasm and banter by watching Jon Stewart... Somoene with a better grasp of communication, please feel free to add or correct anything if I'm wrong...