Was I driving more than 5 mph under the speed limit, or less than 5 mph under the speed limit?

Question

Suppose I am driving 38 miles per hour in a 45 zone. This, of course, is seven miles per hour under the speed limit. Of course, I am driving this slowly because the road is wet, and safe driving habits suggest that when the road is wet, one should consider the safe speed limit to be five miles per hour less than the posted limit.

For this situation, which is correct?

• "I am driving more than 5 mph under the posted speed limit"
• "I am driving less than 5 mph under the posted speed limit"

To support the first case: my speed discrepancy from the posted limit is more than 5 mph. TO support the second case: my total speed was less than 45 less 5 (equals 40).

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Edit: As many pointed out, there are certainly ways to assemble a phrase to remove any ambiguity. But that's not really the point of why I asked. My reason for asking is two-fold:

1. The scenario came to mind when I was driving after a recent snowfall. I was minding my speed, but thought about accident situations. I wondered what would happen if I got in an accident and told the officer, "officer, I was driving more than 5mph under the speed limit." Would that indicate careful or safe driving? Could that phraseology be used against me? Would the insurance company clamp down on that usage of a phrase to deny a claim?
2. More generally, how do comparisons work? There are (at least) two comparisons in either construction: "under the posted speed limit," which unambiguously means "slower than the legal limit," and "more/less than 5 mph." However, in this case, "5 mph" isn't a speed at all; it is a discrepancy. One cannot drive at a speed discrepancy; in fact, the only reason the quantity "5 mph" has units at all is because of the mathematical property that units be additively consistent (i.e. you cannot add 5 mph to 17 bananas). Restructuring the phrase to use a dimensionless quantity also removes ambiguity: "I was driving slower than 89% of the speed limit."

So my question could really be more abstractly framed as: when relatively comparing something to another comparison, does the "relational arrow" point in the direction of the inner-most comparison?

Other examples:

• It is less than 5 degrees below freezing (29 degrees, or 23 degrees?).
• I am more than 5 pounds below my target weight of 180 lbs (177 lbs, or 172 lbs?).

Answer 1

I think the other answers have missed a key factor in how this would be interpreted. And that's that it's a lot more common to be talking about your speed in relation to the national speed limit than to be talking about your speed in relation to 5mph less than the speed limit.

In other words it is unusual to say that your speed was "less than (national limit - 5)", whereas it's fairly common to quantify how much less than the national speed limit you were.

So I think that

I was driving more than 5 mph under the posted speed limit

is very clear that you mean that's how much you were under the limit by. In fact it took me a little while to find your other meaning at all.

Edit: David Richerby makes another excellent point: if you were indeed saying that your speed was "less than (national limit - 5)" you would say "I was driving at less than (national limit - 5)". Not "I was driving less than (national limit - 5)". Further evidence for the ambiguity being negligable in this instance. Do read his answer.

Answer 2

If this were programming, parentheses would help to disambiguate:

"I am driving (more than 5 mph) under the posted speed limit."
"I am driving more than (5 mph under the posted speed limit)."

Thus the same sentence can be parsed such that it means both what you're intending, and the opposite. Same goes for the second phrasing, with the same grouping logic.

That being said, English is not programming. Your first statement ("more than 5 mph under") sounds more intuitively appropriate for the meaning that you're trying to convey.

You could also try to avoid "more than" or "less than" entirely, in favor of a disambiguating word choice:

"I am driving slower than 5 mph under the posted speed limit."

Answer 3

You were driving more than 5 mph under the speed limit. To get there, you subtracted your speed from the limit, giving you 7 mph under. This is more than 5, so there you go.

Answer 4

While one of the two could be considered correct (I would say the first one), there is as you observe a potential for misunderstanding. You can remove that by slightly permuting the first phrase:

I was driving under the posted speed limit, by more than 5 mph.

This also has the advantage of first stating the main point (your speed was under the posted limit) and then quantifying that statement by an estimate of how much you remained below the limit, rather than starting with a quantification for a statement that has not yet been made.

Answer 5

I don't agree with most of the answers. Firstly, there is a syntactic ambiguity, but everyone has shown the parentheses incorrectly.

Secondly, there are three interpretations, not two.

The syntactic ambiguity only makes a difference between the third interpretation hitherto not discussed, and the other two that have been discussed.

We can have two independent clauses which modify "driving":

( I am driving ) ( {more|less} than 5 miles per hour ) ( under the posted speed limit)

This makes two comments about driving: it says that I am driving at some speed that is more or less than 5mph, and that I'm driving under the posted speed limit.

In writing we would use a comma, which should translate to a difference in speech, such a pause or intonation, but these could be lost. Also, we are likely to use a coordinating conjunction: "I am driving more than 5 miles per hour, yet under the posted speed limit". One reason we reject this interpretation is that 5 mph is small. If the sentence were: "I am driving more than 30 mph, under the posted speed limit" this interpretation comes more strongly into play.

The other parse is like this:

( I am driving ) ( {more|less} than ( 5 miles per hour under the posted speed limit ) ) )

and the remaining ambiguity is purely semantic.

The phrase "5 miles per hour under the posted speed limit" has two semantics: it can denote an absolute speed related to the reference (the speed L - 5), or the difference relative to the reference (the difference 5). The focus is either the 5, or the absolute speed formed by subtracting 5.

Perhaps there is a subtle syntactic difference between the two interpretations, but the point is that the whole phrase functions as a unit so anything of that sort is internal to the phrase.

Then the comparative quantifier "more" or "less" applies to one of these two interpretations of the entire unit.

Under the absolute interpretation, "more" means greater than that absolute speed.

Under the relative interpretation, "more" means a greater relative displacement below the point of reference, and so a lower absolute speed.

This is why saying "faster than" or "slower than" instead of "more" or "less" resolves this semantic ambiguity. "Faster than" and "slower than" confirm that the interpretation must be absolute speed, because we never describe a smaller difference in speeds as being faster or slower. 40 mph is 10 below 50, and 39 mph is 11 below 50. We wouldn't call this 11 "faster" than the 10. (However the syntactic ambiguity remains: "I'm driving slower than 5 mph, below the speed limit".)

Answer 6

Neither is correct. Both sentences are ambiguous without context, and should be avoided.

Instead of "I have more/less than X under Y", you should re-phrase the sentence so its meaning is entirely unambiguous.

I am driving slower than 5 mph under the posted speed limit.

I am driving faster than 10 mph under the posted speed limit.

If for some reason you want to avoid the terms above, you can always just include the factual declarations in your sentence. Both the following are correct, and while one will likely feel wrong neither will be ambiguous.

I am driving 37 mph, which is more than 5 mph under the posted speed limit of 45 mph.

I am driving 37 mph, which is less than 5 mph under the posted speed limit of 45 mph.

Answer 7

For this situation, which is correct?

"I am driving more than 5 mph under the posted speed limit"
"I am driving less than 5 mph under the posted speed limit"

I think the first statement is correct, and would not be misinterpreted in most cases.

If you want to use the second construct, you could disambiguate it by saying something like "I am driving slower than 5 mph under the posted speed limit".

Answer 8

You wouldn't say "I was driving more than the speed limit"; you'd say "I was driving at more than the speed limit." On the other hand, "I was driving under the speed limit" is fine. So the natural parsing is that you're quantifying how far under the speed limit you actually were: "I was driving (more than five mph under) the speed limit."

Also, it would be rather unusual to say "I was driving faster than some amount slower than the speed limit." I can't think of a situation in which that would be relevant. The converse situation, driving at less than some amount above the speed limit can be relevant since most jurisdictions allow some slack. However, "I was driving less than 10% faster than the speed limit" evaluates to roughly the same thing for both parsings: "I was driving less than (10% above the speed limit)" means I was doing something between zero and 50; "I was driving (less than 10% above) the speed limit" suggests something between 45 and 50. In both cases, the key fact is "I wasn't doing more than 50mph, officer!"

On the other hand, because the sentence is a little hard to parse and could be misunderstood, it would be better to rephrase it anyway: "I was driving slower than 5mph under the limit", "I was doing less than 40 in a 45 zone", etc.

Answer 9

The subject of your sentence is the posted speed limit.

How I see the sentence;

• "[I am driving more than 5 mph under] the posted speed limit" indicates <40mph
• "[I am driving less than 5 mph under] the posted speed limit" indicates >=40mph

To reverse the logic, and change the subject to the difference between the speed limit and your speed, add at to your sentence;

• "I am driving at more than [5 mph under the posted speed limit]" indicates >=40mph
• "I am driving at less than [5 mph under the posted speed limit]" indicates <40mph

Answer 10

It is unfortunately a matter of parsing priority, effectively we could either take the phrase to mean we are defining a speed 5 miles under the speed limit and we are under it, or that we are an indeterminate number equal to more than 5 under the speed limit. Effectively both are ambiguous phrased as there. Instead we could say: The speed limit was more than 5 miles over my speed. However that would sound less elegant and in reality it is unlikely anyone would actually be confused by this.

Answer 11

Both original choices are bad. First, I don't know what would be the grammatically correct interpretation of each sentence, or if there even is a grammatically correct interpretation. I think the first two responses contradicted each other. Therefore, I don't know what each sentence means, when interpreted correctly. But even if I did, I don't know whether the person making the statement knows it. So even if I know what the statement says, I still don't know how fast the person was driving.

Answer 12

I agree with posts that say both sentences work depending on the parsing. So I think a more important question is what is the 'natural' parsing. Lets look at this way:

I am driving (more than) (5 mph) under the posted speed limit.

I am driving (more than) (5 mph under the posted speed limit).

I think its a question of what phrase you want more than to apply to. Do you want it to apply to the whole rest of your sentence or the next word?

For me, when reading, I see more than and then I think, more than what? Which is followed by 5mph. It makes sense to apply it '5mph' before I get a chance to hear the rest of the sentence so I apply it to that and get

I am driving (more than 5 mph) under the posted speed limit.

Usually when I hear something like more than, I don't keep waiting to hear all the possible things it could apply to. When I hear a phrase afterwards that it applies to, I apply it to that phrase and continue listening.

Answer 13

Personally i think it depends on whether you are mentioning it in passing in conversation or trying to defend yourself (in writing).

The first is more likely to be understood correctly in conversation whereas either would be open to misinterpretation if written.

Marcs answer is probably the least likely to be misunderstood when written.

Answer 14

The original 2 statements:

• "I am driving more than 5 mph under the posted speed limit"
• "I am driving less than 5 mph under the posted speed limit"

are somewhat ambiguous and could easily be misunderstood. For example, I'm sure these were not the intended meaning:

• "I am driving more than (5 mph under the posted speed limit)"
• "(I am driving less than 5 mph under) the posted speed limit"

The problem is, in the context the question asker is relating, someone else is writing down what you said. Maintaining accuracy of the "words" is fairly easy. Perhaps they will be writing your words down at some later time, using whatever punctuation "they" feel is appropriate. And what they have written will likely be read and transcribed further by someone else.

I would favor "I was driving below the posted speed limit by at least 5 mph.", and my 2nd favorite would be "I was driving below the posted speed limit by more than 5 mph." ("below" could easily be replaced by "under" in either case.)

In both cases, there would be a natural pause after the word "limit". But even without a pause, it's clear what is meant.

Answer 15

I prefer,

"I am driving, at least, 5 mph under the posted speed limit"

because

"I am driving 5 mph under the posted speed limit"

Makes perfect sense, in itself, but implies that it is exactly 5 mph.

If we are trying to emphasise that it could even be less that that speed. Using, at least, doesn't introduce a possible double negative or a positive and negative more than 5 MPH under which seems to cause reader to stop, think, back-track, re-read, to work it out.

It also aligns well with logic and mathematics, in that I would write the formular,

driving speed <= Speed Limit - 5 MPH

at least uses fewer words than, less than or equal to .

Answer 16

If you want to get your point across to the cop, "I was driving well under the limit." If you want to explain why, "I was driving well under the limit because conditions were so bad" should do the trick. The margin between your speed and the posted limit is incidental to the main message as you want and need the cop to understand it, so why mention it?

If expressing the size of the margin truly matters to you, try another tack, such as "fully" to emphasize a substantial margin and "only" for a slight one: "I was driving fully 5 miles under the speed limit" or "I was driving only 5 miles over the speed limit." (When spoken, "miles" will be understood in this context as "miles per hour." In print, replace it with mph.)

Answer 17

The trouble with English (sometimes) is that it is interpreted according to context, not just according to grammar and punctuation and sometimes it's even necessary to understand the state of mind of the speaker to judge what it meant. This is (partly) why natural language computing is so hard.

At least in the UK, sticking under the speed limit is a big deal. There are camera, points (not the sort that lead to prizes) and fines. The writer wants to say something about being under the speed limit. If we parse the sentence as:

"I am driving more than (5 mph under the posted speed limit)"

then the writer gives is no idea whether he's speeding or not, which seems unlikely to be his intent. The freezing example is, for that reason, rather more ambiguous.

Answer 18

The answer is a VERY simple lesson in grammar. The basic sentence is the statement "I was driving under the speed limit." The words 'more' and 'less' are adverbs which modify the quantity '5 mph.' Since the difference between 38 and 45 is greater (more) than 5, the correct adverb usage would be 'more than 5mph' under the speed limit.