In patent English, I sometimes encounter 'a length of the surface', 'a length of the surface' or 'the length of the surface,' for example.

I think that you use 'a length of' when you are talking about a specific unit of a measurement. And you use 'a length of' to indicate 'a length of an object(which is not specified)'. On the contrary, you use 'the length of' when you are talking about 'the length of a specific object' or 'the length of the object which was mentioned before.'

Have I understood it correctly?

please explain this in detail with examples. I would really appreciate it.

p.s. Is the same explanation applied to 'height, weight, and size'?

  • You are correct. This is actually the same as "a" versus "the" in almost any context. "A cat" refers to a singular cat in general or to any single cat; "the cat" refers to a specific cat. Jan 6 '15 at 8:59
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    I think a length of the surface is uncommon, and probably will need appropriate context. In any case, this could be the case of a "length" (of the surface) meaning a "piece" of some part of the mentioned surface, not the length of the surface. See Macmillan length "3. [countable] a piece of something that is long and thin - a length of pipe/rope/string". Jan 6 '15 at 9:43
  • @David - Except "the cat" can also refer to cats in general: The cat is a very interesting creature. Or: Of all the household pets, my favorite is the cat.
    – J.R.
    Jan 6 '15 at 11:21
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    @DamkerngT. - Appropriate context in this case seems to be a patent. I looked up "a length of the surface" on Google, and (aside from this question), almost all the hits were from patent documenation, like this one.
    – J.R.
    Jan 6 '15 at 11:32
  • "please explain this in detail with examples" How about you give us some examples and some details of what you are talking about. You haven't provided anything definite to work from - just a sentence fragment. No examples of how it is actually used. Jan 30 at 19:37

It makes sense that we'd find the less common a length of in patents because patents are describing a very generic case.

Let's assume I've invented something that allows me to polish guitar strings, and I market this product as Strolish (short for string polish).

When telling someone how to use the product, I would probably use the definite article:

Put a dab of Strolish on a soft cloth, and gently rub it down the entire length of each guitar string.

However, when I'm applying for my patent, I would use patent jargon. I'm no patent expert, but I wouldn't be surprised to hear my patent lawyer advise me to use different language when applying, including making the language as general as possible:

Strolish puts a lasting, high-gloss shine down an entire length of a guitar string.

It is remarkable how many Google hits for "a length of the surface" were found in patents:

enter image description here

That said, it's quite hard to dissect an actual usage, because most patents are rather technical and difficult for the layman to understand – like this excerpt from U.S. Patent 7276737:

Hence, the smallest ratio of a length of the base of transparent optical element 2 to a length of the
surface 18 of light emitter 4 is preferably greater than about 1, more preferably greater than about 2.
For example, in various embodiments a light emitter 1 mm long may be bonded to a hemispherical
optical element 2.5 mm in diameter and 1.25 mm tall at the center; a light emitter 2 mm long may
be bonded to a hemispherical optical element 5 mm in diameter and 2.5 mm tall at the center; and
a light emitter 3 mm long may be bonded to a hemispherical optical element 7.5 mm in diameter
and 3.75 mm tall at the center


Articles are annoying!

But when we use the indefinite article, we refer to the things in general.

A length of a surface

will refer to any length of any surface. For example if you are talking about some protocol or dimension rules. So, when you talk about those rules, you refer to any surface or any length.

You may say... a length of a surface should be in proportion to ...[anything]

A quick trick is -if I ask you, which surface/length, you won't have any specific thing in your mind and you may reply... any!

On the other hand, the moment you introduce the definite article, things become personal! I mean then you have to specify which length/surface you are talking to.

The length of the surface should be measured first to get the work done (maybe, you are planning for a full size carpet)

You and I know which length and surface you are talking about. Here, the uncertain article won't work!

Yes, it applies to all those dimension parameters.

A size of a TV depends on how big hall you have

You are talking about it generally.


The size of the TV is much smaller as compared to the hall we have.

You are very clear about which TV, hall, size you are talking.


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