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For All Practical Purposes (FAPP) is a pragmatic approach towards the problem of incompleteness of every scientific theory and the usage of asymptotical approximations.
Usually, when a physicist makes an approximation - which can't be justified on rigorous grounds - he tends to justify it by saying that the results obtained are good for all practical purposes (FAPP), meaning that they agree with our experience and approximation errors cannot be detected in practical measurements (for instance, if the error is smaller than the measurement resolution).
FAPP theories are incomplete or lackly-based theories that nevertheless have very high agreement with experiments and tend to be very useful for all practical purposes.
Famous quotes containing the words practical and/or purposes:
“Not many appreciate the ultimate power and potential usefulness of basic knowledge accumulated by obscure, unseen investigators who, in a lifetime of intensive study, may never see any practical use for their findings but who go on seeking answers to the unknown without thought of financial or practical gain.”
—Eugenie Clark (b. 1922)
“I find that the respectable man, so called, has immediately drifted from his position, and despairs of his country, when his country has more reason to despair of him. He forthwith adopts one of the candidates ... as the only available one, thus proving that he is himself available for any purposes of the demagogue. His vote is of no more worth than that of any unprincipled foreigner or hireling native, who may have been bought.”
—Henry David Thoreau (1817–1862)