In theory, there is no difference between theory and practice. But, in practice, there is.

A theory has only the alternative of being right or wrong. A model has a third possibility - it may be right but irrelevant.

A theory has only the alternative of being wrong. A model has a third possibility — it might be right but irrelevant.

In theory there is no difference between theory and practice. In practice there is.

A theory can be proved by experiment; but no path leads from experiment to the birth of a theory.

A theory has only the alternative of being right or wrong. A model has a third possibility: it may be right, but irrelevant.