Welcome to the new version of the Patents Manual. Please note there are changes to the numbering and sequence of the chapters and pages in the manual. You are encouraged to take the time to explore and familiarise yourself with this new structure. 'Substantially', 'about', and 'generally'

Date Published


The word ‘substantially‘ is permissible provided it conveys the necessary meaning (Leonardis v Sartas (1996) 449 FCA 1). ‘Substantially‘ merely indicates that the term it qualifies should not be read too literally. As explained by Blanco White, Fifth Edition, at pages 2-112:

"If draftsmen and judges were perfect ‘substantially’ would have no effect; as it is, the indication is often a useful one. But the word can only mean ‘nearly enough for the patentee’s purposes’, unhelpfully unless the body of the specification tells the reader what those purposes are and what sort of precision is needed to achieve them."

See also Young v Rosenthal 1 RPC 29.


The word ‘about‘ is often used to qualify numerical quantities to indicate that small variations from the specified value are envisaged. It indicates that the specified value is not to be construed as a precise value.

In Catnic Components Ltd v Hill and Smith Ltd (1982) RPC 183, the term ‘extending vertically’ was construed in context as meaning ‘near enough to vertical to enable ...’.

When ‘about’ is used to indicate a variance, the extent of that variance depends on what the skilled person would understand is intended. The precision of the quantity would also have a bearing. For example, ‘about 10‘ might permit a variance of several units, but ‘about 10.301‘ would only permit a variance of a small fraction of a unit.

The use of ‘about’ to qualify the extent of a range, for example, ‘about 10 to about 20’ or ‘about 10 to 20’ does not in itself make the scope of the claim uncertain. The extent of variation indicated by ‘about’ is likely to primarily depend on the size of the range (in addition to numerical precision). For example, a range of ‘about 10 to about 1,000’ would reasonably permit variance of many units at either end of the range. However, a range of ‘about 10 to about 12’ would reasonably only permit a variance of a fraction of a unit at either end of the range.

In all cases, the ultimate question to ask is whether the skilled person would understand the scope of the monopoly.


The term ‘generally‘ raises similar issues to ‘about‘, it indicates that some degree of variation from the specific is intended.

For example, a material that is ‘generally transparent‘ could be totally transparent, or partly transparent, but not totally opaque.

The degree of variation will depend on what the skilled person would understand is intended.

The term ‘generally transverse‘ did not give rise to any difficulties of construction in Nicaro v Martin (1990) 16 IPR 545.

Amended Reasons

Amended Reason Date Amended

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