Not every new idea can be patented, and an invention can encounter patentability problems for several different reasons.
Some Subject Matter Is Outside Patent Protection
Some subject matter falls outside patent protection when claimed by itself. Examples include laws of nature, natural phenomena, and certain abstract ideas. A practical technological application involving one of those concepts, however, may present a different patent-eligibility question.
An Idea Alone Is Not Enough
A general idea or desired result is also usually not enough. Saying "reduce wheel slip" or "use artificial intelligence to diagnose disease" describes a goal. A patent application generally needs to describe and claim a specific process, system, device, composition, or other implementation.
Prior Art Can Prevent Patentability
Prior art creates another limitation. If one earlier reference already discloses every limitation of a claim, that claim may not be new.
Obvious Variations May Not Be Patentable
Even when no single reference contains the entire invention, the claim may still be unpatentable if the difference would have been obvious.
The Application Must Support the Claims
The application itself also matters. An inventor cannot simply add a new technical feature later because that feature would distinguish the prior art. The original application must adequately support the subject matter being claimed.
Claims must also define the invention with sufficient clarity.
For that reason, "the invention cannot be patented" is often too broad a conclusion. Sometimes a particular claim is too broad, while a narrower claim directed to a specific feature, relationship, or combination may still be available.