Economics is not logic and therefore not true or false

Mark Thoma linked to an article by Edward Prescott (of RBC aka Kydland-Prescott and HP filter fame) which I haven't read. I made it through the abstract to this sentence:

Reality is complex, and any model economy used is necessarily an abstraction and therefore false.

This is a dumb sentence. It either has zero content or is wrong. Prescott is probably using it to defend his RBC theory against the fact that it doesn't really match up with empirical data, but even then it's still a dumb sentence. 
First: abstractions are not falsehoods (i.e. antonym of tautology). They are abstractions. All of mathematics is an abstraction, but 2 + 2 = 4 is not false. An abstraction may be an approximation of reality with varying degrees of usefulness. But usefulness is a continuum, not a Boolean.
Second: approximate theories are not false. This is the same sense of "false" that (apparently) Popper viewed Newtonian physics compared to Einstein. People who know the theories understand that one is an approximation to the other with a certain scope. How would calling an approximation "false" be helpful? What do we learn from the sentence (translating):

Reality is complex, and any approximation used is necessarily approximate and therefore approximate.

I hope you wrote that down in your copybooks. It's going to come in handy never. You can capture the same idea by saying "we haven't really figured economics out yet". Really? You don't say ...

This dumb sentence comes from a dumb view of economics; Brad DeLong gives us a quote from Keynes that encapsulates this dumb view:

It seems to me that economics is a branch of logic, a way of thinking ...

No it's not. It's an attempt to see if a real world system involving numerical quantities has regularities expressible in terms of mathematics [1]. You can use logic in economics, but economics is not a branch of logic. If it was a branch of logic, you could do economics without ever collecting data. This is something that is false in a useful sense of the word.
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Footnotes

[1] I do always find it funny that people think economics has too much math. Are they ok with physics having that much math? Well physics doesn't even have any explicit numbers -- all of the numbers in physics are made up (human defined) quantities. Gravitational acceleration on Earth is 9.8 m/s/s. But we made up meters and seconds. Economics can actually have explicit numbers: e.g. two widgets for six tokens of money. You can count them.