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Writing a patent application (page 5 of 8)

From: Canadian Intellectual Property Office


The claims you make in your application are the legal foundation that protects your patent. They form a boundary around your patent that lets others know when they are trespassing on your rights. You define the limits of this boundary with the words and phrases in your claims.

Your claims are key to getting complete protection for your invention; therefore, you may wish to work with a professional patent agent to make sure your claims are properly drafted.

When you write the claims section, you should consider the following:

The scope of your claims

Each claim should have only one meaning, which can be either broad (general and high level) or narrow (more specific), but not both at the same time. Writing many claims, where each one has its own scope, means you can get legal title to several aspects of your invention.

Here is an example of a broad claim (claim 1) found in a patent application for a collapsible tent frame.

Claim 8 for the same patent is narrower in scope and focuses on a specific aspect of one part of the invention. Try reading through the claims for this patent and notice how the section begins with broad claims and then moves towards claims that are narrower in scope.

Look at another example. In this patent application for an electrical connector, the first claim keeps getting referred to by later claims. This means that all the features in the first claim are also included in the later claims. As more features are added, the claims become narrower in scope.

The characteristics of your claims

Three things you should work toward when you are writing your claims are to make them clear, complete and supported.

Your claim must be clear so that you do not cause the reader to wonder about the claim. If you find yourself using words such as "thin", "strong", "a major part", "such as" or "when required", then you are probably not being clear enough. These words force the reader to make a judgement based on their opinion rather than on objective observation.

Each claim should be complete so that it covers an inventive feature and have enough elements around it to put the invention in the proper context.

The claims have to be supported by the description. This means that everything about your invention that you discuss in the claims must be fully explained in the description. Also, any terms you use in the claims must either be in the description or be clearly suggested by the description.

The structure of your claims

A claim is a single sentence (statement) made up of three parts: the preamble (or introductory phrase), the body (or purview) and the transitional phrase.

The preamble (or introductory phrase) names the category of the invention, and sometimes the purpose (for example, a machine for waxing paper, a composition for fertilizing soil).

The purview (or body) of the claim lists the main parts of the invention, such as parts of a device, steps of a process method, ingredients of a composition or groups in the chemical formula of a compound.

The transitional phrase joins the previous two parts. It is made up of words and phrases such as:

Note: The transitional phrase describes how the body of the claim relates to the introductory phrase. The transitional phrase is also important in assessing the scope of the claim as the phrase can be restrictive or permissive in nature.

In the following example, "A data input device" is the preamble, "comprising" is the transitional phrase, and the rest of the claim is the body.


"A data input device comprising:

Keep in mind

Should the Patent Office object to one of your claims, it does not mean that the rest of your claims are not valid. Each claim is judged on its own value. This is why it is important to make claims on all aspects of your invention; doing so is a way of making sure that your invention receives the most protection possible. Here are some tips on writing your claims. Once you have finished this section you have only the abstract and petition left to write!

Tips on writing claims

Here is a summary that will help you write your claims:

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