If you are still developing the invention, you still might have some elements that make the invention unique already. The provisional would give you a way to get a date on those unique elements, and you could always file an upgraded application later.
In other words, fully describe what you have now, and then file a linked non-provisional application when you can move fully describe the rest.
Inventions do not spring forth whole from the drawing board or workbench. They have elements, and then more elements, and the elements change, and are put together differently and ... the invention develops over time. But, for now, elements one and two are really innovative and, perhaps, key to the invention as a whole. The inventor can conceive elements three and four but their precise form or function are still hazy. Still, elements one and two are really innovative. So it makes legal sense to file a provisional patent application that describes the invention as a whole and, particularly, elements one and two. The date of that filing is the "constructive reduction to practice" for an invention having those two elements. Which comes in handy if someone subsequently files a patent application claiming an invention having those two elements. Another example is when an inventor is still figuring out how many different variations of an element can be used that each make the invention work -- filing a series of provisionals and then one cumulative non-provisional 12 months later makes good sense. I'm sure my colleagues can easily think of more examples of when filing a provisional on a still-developing invention makes sense.
The above response is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
People file provisional applications as a placeholder for their invention. The provisional application buys the inventor one year to finish his invention and to file a non-provisional patent application. If and when the application is granted, the inventor gets the benefit patent protection from the filing date of the provisional application. And depending on what the invention is and the competition in the field, people will file the provisional application for this very reason too
This response will not create an attorney-client relationship.
Q:"I know that you're provisional doesn't get examined but you need to include as much information about the invention. How's a person to do this if they are in developing/ in the development stage?"
A: I do not really understand your lack of understanding on this. A person does this by disclosing as much information as they have at the time in the provisional application at the time they file. If further refinements are made, and another provisional application can be filed disclosing those additional refinements. The usual way we do this is to just supplement the original disclosure and file the combination as a new provisional patent application. Then, prior to the one year anniversary of the original provisional patent application, we file a non-provisional application claiming the benefit of that original application and all of the other intervening applications, provisional or non-provisional that are still copending as of the filing date. It is a fairly simple and straightforward concept that should not cause you much trouble. If you have trouble with the concept, then you should hire a patent attorney to handle these types of strategic decisions for you. It really is just a cost/benefit analysis that is generally rather easy to make although sometimes quite complicated if the technical improvements are of unknown commercial value.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
Short Answer: Your discloser need to be enough to support the claims
According to the law, the "property right" you have in your patent are the claims. the disclosure (including the specification and the drawings and the claims) are the foundation which support the claims. without proper foundation, the claim(s) collapses, or, in legal jargon, the claim is not "enabled." A patent is evaluated fro the point of view of a person of ordinary skill in the art. Therefore, the patent disclosure needs to be sufficient so that one skilled in the field of the invention can arrive at the results (claims.) that you say are yours. With this backdrop, you have an invention that is still being developed. If the details that are still in the development stage are not supported by the disclosure, then they are not "enabled." As soon as you have the additional disclosure that will support the additional claims, then you need to protect it in an additional patent application. Good luck.
The simple big picture reason for these statements is that a provisional application is the quick and dirty version of obtaining the earliest filing date for an invention. If your invention is not fully formed, a provisional is a quick way to obtain the early filing date while allowing you to claim priority to the provisional filing date when a utility patent application (non-provisional) is filed. This is mainly because provisionals require less formalities than non-provisionals.
From the litigation perceptive, provisionals are often helpful in building the validity case because the earlier the filing date the smaller the amount of potentially applicable prior art. This is assuming of course that your provisional application fully supports subsequently filed non-provisional applications (which is particularly important in light of AIA - http://www.uspto.gov/aia_implementation/faqs_first_inventor.jsp).
I do think these decisions can be complex if you consider potential long term use of the patent, licensing efforts, and litigation related activity. You should also look into the switch from first to invent to first to file with AIA.
Inventors file a provisional patent application only after they have conceived the invention and have reduced it to practice. Of course, most inventors keep on working on their ideas and improving their ideas and the invention. Once a provisional application has been filed, subsequent provisional applications may be file in order to capture the new ideas. The best advice is to find a good patent attorney on this site, who can help you prepare the best provisional applications to protect your ideas.