Another situation in which the "two cases" approach is helpful involves claim elements that are difficult to detect in an accused product.  For example, if a patent claims detailed software algorithms, it can be difficult to determine whether they are used in an accused product.  If a patent's claims describe chemical or biological phenomena at the molecular or cellular level, it can also be difficult to determine whether those phenomena are occurring in the accused product.  In these cases, the patent holder will usually have an expert string together evidence intended to show, albeit indirectly, that the claim element is present in the accused product.  Conversely, the expert will often distinguish the prior art because it does not expressly mention the claim element without considering the analytical technique used to prove infringement.  The accused infringer may argue that the analytical approach or evidence used by the patent holder is insufficient to establish infringement, which is fine.  In that case, perhaps the accused infringer can seek and obtain summary judgment of non-infringement based on insufficient evidence or exclude the patent holder's experts based on deficiencies in their analysis.

  

However, if those efforts fail, the accused infringer will want to be able to fight the case based on the approach taken by the patent holder.  For example, the same evidence or analytical approach used by the patent holder's expert to establish the presence of a particular claim element in the accused product may also establish its presence in the prior art.  In order to determine whether that is the case, the accused infringer's expert may have to recreate the prior art devices and perform the patent holder's analysis on it. The patent holder's analysis and evidence may also establish that the patent lacks teachings necessary to render the claims definite and enabled.  For example, if the analytical approach for determining infringement was developed after the patent application was filed, the expert's use of it may suggest that there was no known way to detect infringement or determine whether prior art devices were within the scope of the claims when the application was filed, which could provide a basis for establishing that the claims are invalid for indefiniteness.  The patent holder's expert may also make assumptions or carry out analyses that the inventors never conceived of and which show that they never actually had possession of the claimed invention or enabled it.  For example, if the patent-in-suit issue includes working examples intended to embody the invention, performing the patent holder's infringement analysis on those examples may show that they themselves do not fall within the scope of the claims, which could provide significant ammunition for an enablement and/or written description attack.  Of course, such a result may also be used to discredit the patent holder's infringement analysis. 

Thus, the accused infringer should build a second invalidity case based on the patent holder's method of interpreting and applying the patent claims because it may implicate different defenses and strategies than a case based solely on how the defendant believes the claims should be applied.  If the defendant builds a case based only on how it thinks the claims should be interpreted and applied, it may not obtain prior art, discovery, or expert testimony necessary to support the defenses that are implicated by the patent holder's approach to establishing infringement.  Building a defense based on both of the "two cases" maximizes the chances for success.