The invention must be useful. The differencies between the subject matter for which the patent is desired and prior art must be great enough at the time of invention that the subject matter as a whole would not have been obvious to a person having ordinary skill in the art.
Prior art means public knowledge, previous publications, previous patents, and other means.
One or more steps performed on a material, a composition, or an article to produce a change in its nature or characteristics. An article of manufacture or a manufactured article and includes just about anything made by humans. Can be a chemical compound or a mixture of ingredients or a formulation. This is a paraphrased description of the very basic elements of a patent. More information is available from a variety of sources.