Claim interpretation and the dictionary principle

Article  \  13 Dec 2012

'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean — neither more nor less.' - Through the Looking Glass, by Lewis Carroll. 

The claims of a patent specification define the scope of a patentee's monopoly.  Some inventions can be described using words that have fixed meanings, but many require the use of terms that are more ambiguous. Terms used in claims are usually given their 'plain meaning', but the courts have routinely held that the specification can be used as a dictionary to help with interpretation. This concept is known as the dictionary principle. Therefore, it is common for specifications to include definitions of any terms that are novel, or being used in a specific manner. 

This can be beneficial to a patentee, as claims with unclear terms may be held invalid. But care must be taken not to define terms too narrowly. The flip side of being allowed to use the specification as a dictionary is that the patentee is then restricted to the definition they are given. 

The recent decision of the Australian Patents Commissioner in Securency International Pty Ltd v De La Rue International Limited APO 112 (24 October 2012) highlights how specification definitions can affect claim interpretation. 


Securency opposed the grant of De La Rue International Limited's application on several grounds, including lack of novelty, inventive step and clarity.

The disputed application related to a security device having a microlens array and corresponding microimages which were formed from an anti-reflection structure, a method of manufacturing such a device, and a document incorporating such a security device.  

The Commissioner identified five key features in claim 1: (i) An array of microlenses, (ii) a corresponding array of microimages, (iii) an anti-reflection structure on the substrate formed by a (iv) periodic array of identical structural elements, and (v) a partially reflecting layer on the same side of the substrate as the anti-reflection structure.

Possible definitions

Some terms were easily given their plain meaning, for example a 'microlens' is a lens with a diameter less than 1mm. However, there was some dispute over the term 'antireflection structure'. 

The plain meaning of 'antireflection structure' is any structure that prevents the reflection of light. It is typically a material's properties (e.g. its colour) rather than its structure (e.g. whether the surface is rough or smooth) which predominantly determines whether a surface will reflect light. However, the specification provided a different, more limited definition:

An anti-reflection structure of the type utilised in the described embodiments of the current invention, is any periodic structure that is finer than the wavelength of light and provides a surface layer in which the refractive index varies gradually from unity to the index of the bulk material, and thereby minimises reflections that are associated with sudden changes in refractive index.

Arguments and determination

The applicant and opponent both submitted that the term 'antireflection structure' should be interpreted using the plain meaning of the term, not the definition in the specification. Both parties argued that because the narrower definition was recited in one of the dependant claims, claim 1 should be given a broader interpretation based on the 'presumption against redundancy'. 

The hearing officer disagreed. He held that the dictionary principle suggested the term 'anti-reflection structure' should be construed as limited to a structure with a refractive index gradient. The fact that the description provided a definition for the term outweighed the parties arguments in favour of a broader interpretation. 

The prior art cited by the opponent operated on a different principle to the refractive index gradient used by the anti-reflection structure in the claims, and the opposition was dismissed.  


Although the applicant was successful in defending the opposition, they now have a public decision stating the claims of their patent are of a far more limited scope than it appears they intended. 

This decision confirms that where a definition of a term is provided in the description, that definition will be favoured over the plain meaning of the term. It is therefore important to remember to include definitions that are widely recognised in the art in addition to specialist definitions when drafting patent specifications.