# Difference between "at a frequency of" and "at intervals of"

#### Jinbei

##### Member
Hello everyone!

I'd like to know the difference, if any, between the following three statements.

A: All motor vehicles need to be inspected at a frequency of every two years.

B: All motor vehicles need to be inspected at intervals of two years.

C: All motor vehicles need to be inspected every two years.

"Frequency", I think, indicates the number of times per day, month, etc., while "interval" suggests the same number of days, months, etc. in between an event. Does the statement "C" indicate both frequency and intervals at which to inspect all vehicles. Oh, this is so confusing!

Jinbei

• #### duder

##### Senior Member
Hi Jinbei,

For sentence A, I would say All motor vehicles need to be inspected with a frequency of once every two years.

Sentence B looks ok but to my ears it sounds more natural with a little rearranging: All motor vehicles need to be inspected at two-year intervals. I admit that I don't use this construction often, so perhaps other prepositions besides at could also fit.

To answer your question, I think you are correct in your analysis of frequency and intervals. All the sentences mean the same thing, and sentence C is the most natural in everyday language. Whether you interpret it to refer to the frequency of inspections or the intervals between them doesn't really matter, since there is no difference time-wise.

#### GenJen54

##### Senior Member
Duder has hit the nail on the head with this one. I agree completely with his assessment. Our BE-speaking friends may have a differing opinion, however.

If you are writing this for a more formal paper, I would opt for Duder's re-arrangement of option #B (two-year intervals). If this is for a spoken assignment, then I agree that option C absolutely sounds the most natural to a native-speaker.

Option A does not sound grammatically incorrect, however, it does sound stifled to me.

#### panjandrum

##### Lapsed Moderator
Sorry to introduce a complication, but surely:
All motor vehicles need to be inspected every two years.
... is not the same as:
Each motor vehicle needs to be inspected every two years.

The first suggests a two-yearly inspection of motor vehicles - for example in 2003, 2005, 2007.

#### Jinbei

##### Member
Thanks a lot for your replies!

1) All motor vehicles need to be inspected every two years.
Yes, I was thinking about Japan's motor vehicle inspection system when I wrote it.

2) All motor vehicles need to be inspected at a frequency of every two years.

The phrase "at a frequency of every ..." is used commonly, I think.
I have found many examples of such usage on the Web, including the one below.

These licenses are inspected at a frequency of every two years under the State's inspection policy; whereas, these licenses are inspected every three years under NRC's regulatory program.
(From http://www.hsrd.ornl.gov/nrc/reviews/93nd_ltr.pdf)

3) All motor vehicles need to be inspected at intervals of two years.

The phrase "at intervals of ..." may not be common, but is used.

At intervals of three years Member States shall send to the Commission a report on the implementation of this Directive, paying particular attention to the national strategies to be set up in pursuance of Article 5". (From the web page of the UK Parliament)

I think many technical documents, such as operation and maintenance manuals, are required to give specific instructions that are precise and accurate. My three examples may mean the same thing in day to day conversation (two of them may not be used at all), but they are certainly used when there is a need to make a specific difference.

Many thanks again as I've learned a lot from you.
Jinbei

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