If prior art discloses a category that comprises X but does not disclose X itself, can you claim X?

The scenario described hinges on the concepts of anticipation and obviousness in patent law. When prior art discloses a category that includes a specific item (X) but does not explicitly disclose that item, claiming X depends on its relationship to the known art.

In this case, since the prior art does not directly reveal X, it does not anticipate the claim. Anticipation requires that the claimed invention be fully disclosed in a prior art reference. However, the relationship between the unspecified element (X) and the broader category does open the door to the notion of obviousness.

If X is not explicitly mentioned in the prior art, but someone skilled in the relevant field could readily deduce X from the prior art's disclosure, then a claim for X could be rejected based on the grounds of obviousness. This evaluation would consider whether it would have been obvious for a person skilled in the art to arrive at X, given what was known previously.

Essentially, the claim for X stands a chance if it is judged on the basis of whether it is obvious from the combination of the prior art references. Therefore, without additional explicit disclosure of X, the likelihood of invalidation under obviousness is a key consideration for the patentability of the claim.