1. Electricity has a velocity (that is) as high as light’s.

  2. Electricity has a velocity (that is) as high as light’s is.

These two sentences both seem to be correct to me, but I am in doubt about the second one. If the latter is erroneous, could someone explain why?

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    Why do you doubt the second sentence? What do you feel is wrong? Please read the section "How can I ask about checking my text?" in the Help pages. – Andrew Leach Jul 19 '17 at 8:36
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    Have you considered using parallism: Electricity has a velocity (that is) as high as light has. – MetaEd Jul 20 '17 at 23:17
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    You should really be posting on English Language Learners and I have voted to close your question. Whether or not the sentences are grammatically correct they are not English usage. As well as talking about "the speed of light" (as in one answer) I would always say "as great as" rather than using "high" as the common phrase is "greater than the speed of light". – David Jul 23 '17 at 9:00
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    I just want to point out that the statement about electricity being as fast as the light may be misguiding since it does so only when you think of it as an electromagnetic wave. However, this is usually not the kind of "electricity" that people have in mind when they hear that word. Much more often it is either "the juice that powers up our TVs and fridges.", i.e. the speed of energy propagation in circuits, or alternatively, the speed of electrons. Both of those are much, much slower. You can read more here. – undercat Jul 30 '17 at 23:14
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    Thank you @undercat for your comment. I started to write a comment and got sidetracked. The OP may wind up with a sentence that is grammatically correct, but which makes no sense. Light is an electromagnetic wave. I don't know what the OP wants to say. – ab2 Jul 31 '17 at 0:51

This answer ignores the physics implied by the sentences and focuses only on the English content.

In linguistics, ellipsis (from the Greek: ἔλλειψις, élleipsis, "omission") or elliptical construction refers to the omission, from a clause, of one or more words that are nevertheless understood in the context of the remaining elements. - wikipedia

Consider the sentences as elliptical constructions. Here are the sentences with plausible suggestions (in italics) for the 'omitted' words:

1a. Electricity has a velocity (that is) as high as light's velocity.

2a. Electricity has a velocity (that is) as high as light’s velocity is high.

Your question is whether your #2 sentence is erroneous. As the above demonstrates, the sentence is grammatically sound because it provides enough context to fill in the 'missing' terms.

  • Should we consider to use definite article "the" in "Electricity has THE velocity (that is) as high as light's velocity", as there is a clause to modify that velocity? – dan Aug 2 '17 at 23:52
  • @dan No, an indefinite article sounds better. I'm not sure why exactly. Perhaps it's that the construction 'a P as high as Q' admits many (potential) P's. You might want to ask a separate question about that. – Lawrence Aug 3 '17 at 23:54

I think you would come across much more clearly, if you instead structure this as "Electricity travels at the speed of light". The term velocity gets in the way of clarity in my opinion. This is particularly the case if your intended audience includes people who are not physicists or engineers.

By definition, velocity is a physical vector quantity; both magnitude and direction are needed to define it. But electricity in the real world is often transmitted along distribution networks with junctions. Therefore not all electricity travels in a straight line. So the concept of velocity perhaps clouds the central concept that you want to express.

  • Electricity is just the general idea of phenomena associated with electric charges. Real world phenomena such as electric currents can be described with vectors. Electrons can travel at certain speed and direction, that is , with certain velocity. The same principle is applicable to light: just replace electrons with photons . So, that's not the problem. The problem is to compare vectors directly in terms of "height" or magnitude. That's like saying that the south is higher than the east. That makes no sense. The comparison should be made in terms of speed, magnitude of velocity. – Alex Sarmiento Jul 28 '17 at 7:30

The standard way of expressing this idea, at least in BrE, would be "Electricity has a velocity as high as that of light".

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    This doesn't sound at all idiomatic. Why is that the correct way? – marcellothearcane Jul 19 '17 at 9:06
  • It sounds fully idiomatic to me (AmE), although I agree that "as great as" would be better than "as high as." In the context in which this sentence would occur, "a velocity as great as light's" would be, to me, wrong register. – Xanne Jul 28 '17 at 8:46

I think Lawrence has already given the correct answer, but let me try to make it simpler by 'breaking down' the meaning of the sentence:

(1) you are comparing the velocity of electricity with the velocity of light.

(2) the velocity of electricity is the same as the velocity of light, is the simplest statement of the implied meaning, which we can state in different ways. Your statement:

Electricity has a velocity (that is) as high as light's (is).

(3) If you want to break the sentence down...

Light's velocity is high.

Electricity's velocity is just as high.

Electricity's velocity is as high as light's (velocity) is (high.)

It is acceptable to drop the repeated 'velocity' and 'high' which are implied, and write it as

Electricity's velocity is as high as light's is


Electricity has a velocity (that is) as high as light's is.

Thus your second sentence is grammatically correct, and follows the same structure as these random examples:

A mobile phone is as expensive as a gold watch is.

Tom is as clever as Walter is.

He is as rich as she is.

...and finally, considering that the final 'is' would be just as implied and superfluous (as 'velocity' and 'high' are), you can therefore drop the final 'is' as well, for consistency, and thus you get your own first sentence:

Electricity has a velocity (that is) as high as light's.


TL;DR: The "is" is implied by the apostrophe and the rest of the sentence and just kinda leaves another clause incomplete in the sentence.

To answer you're question, we're going to need to deconstruct the sentences into their components and talk about what all is communicated by each chunk.

But first, let's do future readers a favor and lose some of the specifics of the sentence so we can get rid of superfluous variables(1). I'm thinking of four elements in this sentence. The first two, electricity and light, can be removed and we'll substitute them with {noun_1} and {noun_2}, respectively(2). The third element that we should cut out is the "(that is)" because ultimately it suffers from the same issue that the question is asking about. The fourth is velocity, velocity is a quality of electricity, so we're going to just call it {quantitative_descriptor}(3).

This leaves us two sentences:

  • {noun_1} has a {quantitative_descriptor} as high as {noun_2}'s.
  • {noun_1} has a {quantitative_descriptor} as high as {noun_2}'s is.

Okay, let's take a look at the apostrophe following {noun_2}. What all does that apostrophe entail? Firstly it entails possession but that's the low hanging fruit here. What is it possessing? It is possessing the {quantitative_descriptor} whose value(in this case height) is equal to that of {noun_1}. Okay, but how does this relate to the is that's tacked onto the end of OP's second example? It means the "is" is repetitive because the apostrophe implies that not only does the {quantitative_descriptor} exist but also tells us what the value of that quality is because it is identical to the value of the quality belonging to {noun_1}. Explicitly what the apostrophe means is that:

*{noun_1} has a {quantitative_descriptor} as high as {noun_2}'s is high.

So not only is the "is" repetitive it is also a statement about being without telling us what is. It is an incomplete clause in effect. However since we already got what was implied by the apostrophe we understand it.

When would you use the is? When you're going to change what quality the descriptor is describing. For example, "Einstein was as smart as Everest is tall", communicates the change from the implied comparison.

  1. I'm approaching this like a complicated math problem where sometimes you get variables that don't actually do anything, like a section of an equation that ends up being multiplied by 0 ((x^3 + 13mod2 + 100!)*0 + 5 = 5) or something being multiplied by 1( (5*1 + 13 = 18) === (5+13 = 18) ).

  2. I'm substituting them out here because we're not really conditioned to be thinking about light(photons) and electricity(flow of electrons) as things that have a speed because in our lives their perceived as being more or less instant. So in order to clear our brains of unnecessary clutter I'm dropping them here for the sake of clarity. One could just as easily substitute in two different makes of cars or some similar objects.

  3. These variables aren't linguistic terms, I'm just doing my best to describe the role each one is playing, I'm a programmer not a linguist so please forgive me for not using the right words.


from my opinion, both seem not correct. I would think "Electricity has a velocity as high as light does" is correct to me. someone is welcome to correct me if I get it wrong.

  • The 1st one is definitely correct, since it is from the native speaker. Your own sentence is also correct (because it follows grammatic rules). – Anti-American Anti-Zionist Jul 19 '17 at 7:14
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    Grammatically, both "Electricity's velocity is as high as light's." and "Electricity has a velocity as high as light does" seem correct to me, because "Electricity" and "light" share the same structure. Need grammar experts to clarify :) – dan Jul 19 '17 at 7:35
  • @Tug'tekin, just a note, a native speaker can make statements with incorrect grammar just as a non-native one can. Just because a native speaker said it doesn't make it "definitely correct." – vpn Jul 30 '17 at 15:10

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