What must an inventor demonstrate in a patent application?

The invention must be novel. It must not be obvious to the hypothetical person having ordinary skills in the subject matter. It must also have some utility and not be frivolous in nature. Further, it is necessary to demonstrate that the invention can be made operable.

What is a "novel invention"?
An invention cannot be patented if it “was known or used by others in this country, or patented or described in a printed publication in this or a foreign country, before the invention thereof by the applicant for patent” or “the invention was patented or described in a printed publication in this or a foreign country or in public use or on sale in this country more than one year prior to the application for patent in the United States.” 35 U.S.C. §102 This means that your invention cannot have been previously patented anywhere else in the world or described in written form by someone else.

When is an invention obvious?
An invention is too obvious to patent when anyone of average intelligence in that field of study could have invented it themselves. For example, creating scissors with a larger handle size than what is out on the market is too obvious for patenting. However, if you create a new means of cutting, then that would be novel.

Why must an invention have utility?
A patent is meant to protect an inventor of a marketable product. If an invention is unmarketable, or useless to the public, then there is no reason to patent the item. But don't worry: it is exceptionally difficult to invent an item that does not meet the utility requirement. Even items such as lawn flamingos and jumping snails have been determined to have utility and were patented.

Why must my invention be operable?
Operability, similar to utility, is a requirement that goes back to the central purpose of patenting. In fact, the patent office originally required that a working model of your invention be included with your patent application. If your invention is inoperable, it is useless, much less marketable. If you do have a “concept” for an invention that you wish to protect, put your concept on paper and apply for a copyright.