The final substantive stage in the process of getting a patent is the examination stage, where a person from the patent office, the Examiner, will read your application and your claims, and will check the application and claims against the prior art, in other words, what has been done before. Prior art can be patents, patent applications, published papers, or visual material, even including such things as YouTube videos. The Examiner will search both for individual items that appear to be substantially the same as your invention and for multiple items that, in combination, appear to be substantially the same as your invention.
Some terminology: In the United States, if there is a single piece of prior art that appears to be substantially the same as your invention, your invention lacks "novelty". Two or more pieces of prior art which, when combined, appear to be the same as your invention deprive your invention of "inventive step".
What strategies can be used to establish Novelty or Inventive Step?
Some of the more common ones are given below.
1. Show that the invention contains a feature that the prior art lacks, or that all of the prior art lacks, either alone or in combination.
For example, the invention is a sprinkler valve with a manual-off state, where water does not flow no matter what an automatic control does, a manual-on state, where water flows no matter what the automatic control does, and an automatic-control state, where water flows if the automatic control is "on" and does not flow if the automatic control is "off".
The Examiner finds a prior art valve that has all three states (manual on, manual off and automatic).
However, the prior art valve requires two controls to enable all three states (for example, a first control that, when closed, provides a manual off state and, when open, provides an automatic control state; and a second control which, when closed, has no effect on flow and, when open, provides an always-on state.) The invention, on the other hand, can switch between all three states using only one control.
Since there is no way to combine the two controls of the prior art into a single control, the invention, with its single control is patentably different from the prior art.
A similar argument would hold if the Examiner found two prior-art valves, one with manual off and automatic control and one with manual-on and automatic control. Combining the two into a single valve would, once again, lead to a device with two controls, patentably different from the invention.
2. Narrow the patent by adding a feature to the independent claim that the prior art lacks – this is called adding a "limitation" to the patent.
For example, the Examiner has found two prior–art valves. He says that, if one were to take a specified part out of the valve control in one patent and put it into the valve control of another patent, one would get a single-control valve with all three states.
However, the specified part is a plate with passages in it. If one set of passages connects the input to the output of the control, the valve is in its automatic control state. If another set of passages connects the input to the output, the valve is in its always-on state. If neither is connected, there is no flow – a manual-off state.
However, in the invention, the exit flow from the valve control is down the center of the control, while the input flow is from the side of the control. In the prior-art valve, input is from one end of the plate and output is at the other end of the plate. Therefore, if there were flow down axis of rotation of the plate, it would be impossible to switch from one state to another.
Therefore, add a limitation to the independent claim that the exit flow is down the axis of rotation of the valve control, since that is a patentable difference between the invention and any combination of the prior-art valves.
3. Argue that the prior art works in a fundamentally different way than the invention.
For example, the invention is a foldable stretcher with about 5 sections which folds up into a neat rectangular package which will fit tidily into a backpack. The stretcher is wider at one end than the other so the sections nest within each other, making the folded stretcher relatively thin. The stretcher has carrying handles at each end, which rotate into a position alongside the folded sections. The joints between the sections comprise legs which are connected together longitudinally by wires, with each wire extending from the base of one leg to the top of the next leg so that the stretcher is stable in the unfolded state, both while resting on the ground and while being carried. In the folded position, the legs, like the handles, lie alongside the sections. Unfolding the carrying handles tightens the wires and stabilizes the structure.
The Examiner claimed that an earlier patent, if modified by adding bits of two other patents, anticipated the invention. The earlier patent disclosed a bed with a set of legs, diagonally connected together by hinges. Pushing the legs to the center of the bed collapsed the bed into a set of legs and a crumpled piece of canvas.
In this case, one could argue that the set of legs of the bed were connected by hinges diagonally across the bottom of the bed, with the hinges approximately in the middle of the legs. This was fundamentally different from the legs-and-wires of the invention, where the legs were connected by wires, not hinges, the legs were connected together longitudinally, not diagonally, and each wire joined the base of one leg to the top of the next leg, rather than having the joining of the legs approximately in the middle of the legs for all of the legs.
4. Argue that it is not possible for the combination given by the Examiner to work. For example, it can be argued that (a) it is not possible to fit the parts together, (b) although the parts can be fitted together, they will not work together once fitted, or, (c) although they fit together and work together, the result is fundamentally different from the invention. The last can be argued, but it is the most difficult.
For example, for the stretcher above, the Examiner claimed that a combination of two earlier patents would create the invention. One was the bed with a set of legs, as described above. A second was a stretcher where the side poles could be separated into pieces and the whole thing, when taken apart, comprised a bunch of shortish sticks connected together by short pieces of rope (so that you had to connect together the proper pieces when reassembling the thing) surrounded by the folded canvas of the bed part.
Against the combination, it can be argued that there is no way to attach the stretcher to the first bed in such a way as to make a structure with legs connected to the bed sides by hinges (the stricter side poles came apart for folding). The legs of the combination would, like the legs of the bed, collapse into a bundle with all the tops at one end and all the bottoms at the other end, instead of being arranged in the head-to-tail fashion of the invention when folded. Furthermore, the combination, when collapsed, is a bundle, not a set of bed sections nested one within the other.
5. Another strategy involves the number of changes that would be necessary to get from the cited prior art to the claimed invention. I once successfully argued that it would take 17 steps to get from the 3 patents cited as prior to the claimed invention so that, although combining those three patents to form the claimed invention might have been obvious in hindsight, it certainly would not have been so in foresight.
It is usually not a good strategy to argue that the invention lacks something that is in the prior art. As long as it is possible for the prior art to work (even if badly) without the part, the lack is not a patentable difference.
For example, a device for creating a solution of fertilizer in water where a user gets reproducible results by occasionally dumping a bag of fertilizer into a water-filled tank. This is a very simple invention – no screw feeds for the dry fertilizer, no weighing of the fertilizer, no careful control of the feed rate of the liquid going into the tank, no need to ensure that the dry bulk fertilizer remains dehydrated before use. Just make sure that there is always solid fertilizer in the tank and make sure that the water level in the tank doesn't get too low or too high. Also, don't dispense the solution too fast.
Since it is possible to argue that the prior art device will work – even if badly or unreliably – without the screw feed, without weighing the dry fertilizer before introducing it into the tank, and without dehydrating the fertilizer, as long as the fertilizer sits in the tank long enough, the Examiner can say that simplifying a piece of kit is an obvious thing to do, so that it would be obvious to remove the screw feed, etc, from the prior art and get the invention, so that the invention is not patentable.
The strategy of arguing that lack of a feature is a patentable difference can be used if (a) there is no prior-art device which lacks the feature so that everybody knows that devices of this type require the feature, or if (b) the prior art cited by the Examiner states explicitly that the prior-art device can not work without that feature and, preferably, the prior art cited by the Examiner explicitly states that that prior-art devices without the feature are intrinsically unsatisfactory.
Of course, combinations of these strategies can also be effective. A good patent agent will always consider very carefully which strategy or strategies is most likely to be successful and to convince the Examiner to allow granting of a patent for the claimed invention.