Understanding what the Patent Office considers new will not answer the question of what is patentable, but understanding what is patentable nearly impossible without an understanding of what the Patent Office considers new.
Claims are what is evaluated
When the Patent Office considers whether an invention is new the drawings or the description of the patent application are not what is evaluated. The Patent Office considers whether the claims in the patent application describe an invention that is new. A claim is a definition of an invention. More specifically the claim is the definition what an inventor would hope to be able to prevent others from practicing. Claim language can be lengthy and complicated but in most cases the language is drafted such that the definition encompasses the prominent embodiments described and drawn in the application.
Prior Art is the point of comparison
Prior art can come from a great number of sources, but an example would be a patent that was granted prior to the filing date of the relevant application. An embodiment taught by the old patent (the “old embodiment”) would be compared against a claim in a patent application to see if a claim is defined broadly enough to encompass the old embodiment. If the patent application claim is so broad that it includes the old embodiment then the Patent Office would consider the claim anticipated (not new). Conversely, if a claim is narrow enough that it does not include the old embodiment then the claim would be considered novel (new) with respect to the old embodiment.
The “All Elements” Rule
An invention can have many features, but the features that end up being the most important features are the features that are claimed. Patent claims are typically prepared by a patent attorney or patent agent and generally cover commercially significant features of the invention. Claims typically do not contain every feature of an invention. If a patent claim were being evaluated to find out if the claim was novel (new) the required features of the claim would be considered. If the claim required hypothetical features A, B, C, and D and a piece of prior art, such as the old embodiment described above, contained only features A, B, and C the claim would be new with respect to the piece of prior art. However, if the piece of prior art contained each of features A, B, C, and D then the claim would in most cases be considered anticipated or old. In essence, a Patent Examiner would need to find each element required by the claim to reject it as anticipated (old). Patent attorneys and patent agents generally refer to the requirement of finding all elements in a novelty evaluation as the “all elements rule.”
Claim by Claim Comparison
Each claim in a patent application must be novel/new in the eyes of a Patent Examiner for a patent to be granted. In addition to judging an application based on whether the claims are new, the Patent Examiner evaluates many other aspects of the claims including whether the claims are obvious and whether the claims clearly lay out the subject matter that is being claimed.