The last section explained how we could get Inventor John's application mess squared away where he tried to include more than one invention in a single application.

However, to continue with this example, what if a few months after filing the divisional application, John comes up with a great way to make his furnace run more efficiently. So even though he already filed the application, he now wants to add to it to improve on the original invention.

What are his options now? Does he file a brand new application and just drop the original furnace application? Can he keep both? Or should he just forget about the improvements?

Luckily, the PTO thought this through already and as a remedy, created what's called a continuation-in-part (C-I-P) application.

By filing a C-I-P, John can cover the improvements to his furnace invention without having to start over by filing a brand new application.

If he files a C-I-P application, then the improvements will have the filing date of the C-I-P (which would be a later date) while the old material will still keep the filing date of the original which was June 1, 2013.

Keep in mind that a C-I-P always repeats a substantial portion of the earlier application while adding in some new material.   One rule about C-I-P's is that they must be filed while the first nonprovisional application is pending. So, if John waits until after his original furnace application issues into a patent, he would have to file a brand new application claiming his furnace improvements.