According to the Guidelines for the United States Patent and Trademark Office, a claim in a patent application can be rejected as not having a “credible utility”.  Frequently discussed examples include claims for perpetual motion machines or claims for medicines that purportedly eradicate all diseases.  As the thinking goes, if the sole disclosed purpose or function of a claimed invention is simply not believable and is unsubstantiated, then the claimed invention does not satisfy the 35 USC §101 requirement of being “useful”.  The Applicant then has the burden of rebutting, once a showing of no specific and substantial credible utility has been properly established.

However, there might be some actually “useful” part of a disclosed invention, which could be claimed as being outside of the non-credible utility.  If that useful portion of the invention, or use of the invention, satisfies the requirements for novelty and nonobviousness, and is supported sufficiently to add credibility, it might yet satisfy the requirements for patentability.  This is not to say we should seek out perpetual motion machines, miracle cures and other purported inventions that sound too good to be true.  But, there might be something to learn, and there might be something of value hidden within.

An inoperative invention also has “incredible” utility.  Here it may be that a claim is not correctly written, and that the invention itself is operative but the claim is defective.  So, it is worth looking carefully at the claims if they are rejected as not having credible utility or having incredible utility.  Whether the claims should be argued as having actual credible utility, amended to cover some other aspect of an invention with some other aspect of utility, or amended to correct an error in the relationship among the elements, depends on the specifics.  Or, there might be another strategy.  This is part of the art of patent prosecution.