Two other common forms of the fallacy arise from reformulated versions of Fallacy Forms 1 and 2. In Fallacy Form 1, we first replace the clause "X is immoral" with the equivalent clause "not-X is moral." (For example, saying that Crusoe should not neglect his nutrition is equivalent to saying that he should follow principles of good nutrition.) Likewise, the clause "X should be illegal" can be replaced with the equivalent "not-X should be legally required." (Prohibiting bad nutritional habits is equivalent to enforcing proper ones.) With these replacements, Fallacy Form 1 can be rewritten:

"If not-X is moral (or desirable), then not-X should be legally required."

We then simplify this assertion by letting "X" stand for "not-X," thereby arriving at Fallacy Form 3 (at right below).

Fallacy Form 1 (Inverse):

If X is immoral (or undesirable), then X should be illegal.

Fallacy Form 3 (Inverse Reformulated):

If X is moral (or desirable), then X should be legally required.

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