While novelty may be the most complex of the basic patent requirements, nonobviousness is the most difficult. The inventor needs to show that, in light of the state of the art, the invention is not an obvious development . The courts have come up with a three-factor test for examining nonobviousness. A patent examiner or a court will:
- examine the scope of the prior art;
- determine the differences between the prior art and the invention under consideration; and
- look at the level of skill an ordinary practitioner of the pertinent art has.
After doing that, the patent examiner looks to see if a person reasonably skilled in the art would have found the invention to be obvious.  In addition to this, several secondary considerations can be taken into account, including commercial success of the invention, a long felt need that the invention fills, the inability of others to conceive the invention, recognition of the patent by some competitors, and the fact that the invention was formerly described as impossible by those reasonably skilled in the art.  The PTO has been criticized for failing to uphold this standard in the software field, by granting patents to software that was considered obvious by reasonably skilled programmers. The PTO has discussed addressing this problem by expanding their archive of prior art to include more unpatented software.