We have some essays from the early days of the Imperial Patent Office which admit that from all practical issues with respect to the new uniform grant of patents for inventions, the question how to draft claims is the most imperfectly explored topic [1]. Article 20 of the Imperial Patent Law from 25 May 1877 requested that every patent application must comprise a precise indication of the subject matter that shall be protected by a patent. In the law making process the German government explained their motives:


In order to provide for the processing of the patent a solid basis, the application shall precisely state in a specific phrase what the applicant claims, so that the patent office and all concerned parties are not compelled to determine the claim themselves from an extensive description without having the certainty about the true scope of the claim.


Prof. Dr. Ernst Hartig, a professor for mechanics who was occasionally commissioned by the Imperial Patent Office, complained about the abuse of the patent system in the United States. A new machine is dissected subsequently into distinctive elements resulting in a vast number of combinations,  most of which have no practical significance. This explains why in Imperial Germany at the time dependent claims were used very moderately. The Imperial Patent Office commissioned technical experts as examiners on a per case basis. Therefore the examiners were not pleased to spend too much time with a huge number of patent claims. Prof. Hartig pleaded for a first claim of a maximal allowable scope and a second narrower claim for the specific arrangement of construction elements, for which to reference to what is shown in the drawings would be sufficient.        

Since then the art of claim drafting has significantly changed. Rather then remaining in the past I thought it would be interesting to analyse how the historical patent applications of Nicolaus Otto would be processed today if they would have been filed according to the todays requirements of the European Patent Convention.

There would be serious issues today. In the following simulation we first have a look on general issues and then we analyse the main claims 1, 4, and 5 separately.



The EPO would issue a communication pursuant to Article 94(3) EPC (examination report). The first part would be along the lines:

Reference is mode to the following document; the numbering will be adhered to in the rest of the procedure.

D1   FR 43 624 (LENOIR)

The application lacks unity within the meaning of Article 82EPC as it contains the following inventions:

claims 1-3

Introducing into an enclosed space a mixture of combustible gases and air in order to slow down the combustion from gas particle to gas particle

claim 4

Adapting the operation of a piston in a cylinder that for each two revolutions of the crankshaft 4 effects are achieved

No further special technical means are available by means of which a relationship could be established between the subject matter of  any of these two groups of claims.

The subject-matter to be excised may be made the subject of one or more divisional applications. The divisional applications must be filed with the European Patent Office in Munich, The Hague or Berlin and shall be filed in the language of the proceedings relating to the present application (cf. Article 76(1) and Rule 36(2) EPC). The time limit for filing divisional applications (Rue 36(1) EPC) must be observed.

The first part of the examination report raises the lack of unity of invention and provides a suggestion how to be able to pursue all inventions in different applications, i.e. by filing divisional applications. Usually the objection of lack of unity would explain in more detail the reasons. We will however develop these reasons thoroughly in the next  paragraphs ourselves.



Lack of Unity

Article 82 EPC - Unity of invention

The European patent application shall relate to one invention only or to a group of inventions so linked as to form a single general inventive concept.




The basic principle behind the requirement of unity is that a patent is granted for each invention separately, i.e. in order to proceed to grant, a European patent application is required to contain claims relating to one invention only (G 2/92, Reasons 2).

This requirement of unity is further justified by the principle of equal treatment of applicants: any applicant is entitled to the same rendered service against the paid fees, i.e. one search/examination against one search/examination fee.

source: EPO Guidelines for Examination; Part F Chapter V


It is of course a nice argument that applicants are treated equally, but first and foremost all patent offices over the world do not want to miss out on the fees that finance their existence.

Rule 44 - Unity of invention

(1) Where a group of inventions is claimed in a European patent application, the requirement of unity of invention under Article 82 shall be fulfilled only when there is a technical relationship among those inventions involving one or more of the same or corresponding special technical features. The expression "special technical features" shall mean those features which define a contribution which each of the claimed inventions considered as a whole makes over the prior art.



A substantive assessment of unity of invention requires

  1. determining, in the light of the application as a whole, the common matter;
  2. comparing the common matter with the "prior art at hand" to examine whether the common matter makes a contribution over that prior art, namely whether it comprises "special" technical features within the meaning of Rule 44(1);
  3. if the common matter does not comprise special technical features, analysing any remaining technical features which are not part of the identified common matter to determine if there is a unifying technical relationship among some of the claims.

(i) common technical problem

The technical problem in the non-unity assessment may be different from that in a patentability assessment since the overall object is to find out what the claims have in common. When analysing the technical problem in a non-unity assessment, the starting point is usually what is considered by the applicant in the description as having been achieved.

source: EPO Guidelines for Examination - Part F - The European Patent Application - Chapter V - Unity of Invention - 3 Assessment of Unity 

We strip off the claims the features that they do not have in common, so that only (comparable) technical features remain:


Claim 1in an enclosed space combust combustible, with air mixed gases, whereby the combustion products expand by the produced heat and thus release operational power.
Claim 4Sucking in different gas types into the cylinder and combust those and generate work of those;


Comparing the remaining technical features of claim 1 and claim 4 they only common matter that can be established is that in both claims a mixture of air and combustible gases is combusted in an enclosed space in order to produce work by expansion.

ii) comparing common matter with prior art at hand

In this case the common matter is already known from various prior art, in particular from Lenoir. Therefore there is no technical contribution of the common matter to the prior art.

iii) Unifying technical relationship

Generally speaking, the technical problem solved by claim 1 is to improve the smooth running of the gas engine and/or reducing the risk of explosions that eventually may destroy the gas engine. The problem to be solved by claim 4 is to improve the efficiency of the combustion, without being restricted to the features of claim 1. As no unifying technical relationship exists above and beyond the common matter between the group of claims 1-3 and claim 4, the two groups of claim lack unity.


In order to avoid a rejection to lack of unity the applicant has to amend the claims such that the lack of unit does no longer exist. Let's assume the lack of unity was already raised during the establishment of the search report and the applicant has not paid any additional search fees and had indicated to pursue the first group of invention. In this case claim 4 has to be deleted. However, it is possible to make the second group of invention as claims dependent on the first group of inventions, i.e. combine the claims, provided there was sufficient disclosure for this combination in the originally filed application. The claims would look then keeping for the moment the original wording with all the other deficiencies that still will have to be rectified:

  1. Introducing into an enclosed space combustible, with air mixed gases and air of a different kind prior to their combustion in such manner that at a point of an initiated combustion it [the combustion] slows down while [the combustion is] continuing from gas particle to gas particle, whereby the combustion products and the kind of air that envelopes them expand by the produced heat and thus release operational power.

  2. Generating the under 1 pronounced effects with gases which until combustion have atmospheric pressure.

  3. Generating the under 1 pronounced effects with gases which have before combustion more than atmospheric pressure.

  4. Set up the mode of operation of a gas engine according to one of claims 1, 2, or 3 with a crank motion such that for two rotations of the crankshaft of one side of the piston the following effects are generated:

    1. Sucking in the gas types into the cylinder;

    2. Compression of those;

    3. Combustion and generating work of those;

    4. Exiting of those of the cylinder.

  5. The construction of a machine, as described.

"A priori" Lack of unity

In this case, as we know from Otto himself, Lenoir was known to him as prior art. That means that the non-unity of his patent application already existed at the time he was filing his application. This is called a priori non-unity. It is used most of the times deliberately in order to pay only one filing fee, as this gives the option, by paying the fees, to section out the non-unitary invention, as long as the patent is not granted or finally rejected, by paying additional fees.



"A posteriori" Lack of unity

It also happens that at the time of filing there was in the eyes of the inventor a unity invention, but new prior art renders the main claim not novel. In order to illustrate the effect let's assume the following claims:


Claim 1Features A + B known to the inventor, feature C is his invention
Claim 2dependent on claim 1; adds a novel feature D
Claim 3dependent on claim 1; adds an alternative, novel feature E

This results in the following feature map:

Claim 1A + B + C
Claim 2A + B + C + D
Claim 3A + B + C + E

In the eyes of the inventor, at the time of filing, his invention is new, because he only knows of the combination of features A + B and not C. Claims 2 and 3 are automatically new, as any feature added a feature to a claim that is new, narrows the new claim, and therefore shares the faith of the claim it depends on, i.e. it is also new. This is a logical consequence independent whether the added features are new or inventive.

Let's assume now that in the search the Examiner finds prior art which discloses the combination of features A + B + C in a single document but neither feature D nor feature E. Therefore claim 1 is no longer new, but either claim 2 or 3 are still new. In this case a new problem has to be formulated in view of the new prior art. If this problem is solved by either claim 2 or claim 3 then there is unity of invention. However, if no common problem can be formulated because the alternative features D and E solve different problems, then the Examiner will raise the lack of unity deficiency and asks the applicant if he wants to pursue invention 1 (A+B+C+D) or invention 2 (A+B+C+E). This situation is called a posteriori non-unity, as the non unity was not obvious from the filed application.   



Missing category


[1] Dr. Ernst Hartig, "Die Formulierung der Ansprüche in den deutschen Patentsschriften und der wesentliche Inhalt mechanisch-technischer Erfindungen", Der Civilingenieur.