# skid marks

#### hhtt21

##### Key Member
Original: How can we use the skid marks of a car to estimate the car's speed before the brakes were applied."

I think instead of simple past the use of "present perfect" would be better. So what do you think?

Mine try: How can we use the skid marks of a car to estimate the car's speed before the brakes have been applied."

Source: Algebra & Trigonometry by Keedy/Bittinger.

Thank you.

#### GoesStation

##### No Longer With Us
Re: present perfect passive v. simple past passive.

The original is logical: we are now estimating the speed of the car at the time in the past when the brakes were applied.

The present perfect version is not logical. It says that, at a time before the brakes were applied, we will use skid marks that cannot yet exist to estimate the car's speed.

#### hhtt21

##### Key Member
Re: present perfect passive v. simple past passive.

The original is logical: we are now estimating the speed of the car at the time in the past when the brakes were applied.

The present perfect version is not logical. It says that, at a time before the brakes were applied, we will use skid marks that cannot yet exist to estimate the car's speed.
Two two versions seems to me in meaning what you have explained here. It seems to me that the time adverb, before, implies this. So shouldn't it be "after" instead of "before" in two versions?

So I would like to ask what is the difference between

1.we are now estimating the speed of the car at the time in the past before the brakes were applied.
2.we are now estimating the speed of the car at the time in the past after the brakes were applied.

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#### Rover_KE

##### Moderator
Staff member
Re: present perfect passive v. simple past passive.

Isn't that more eye-catching?

#### GoesStation

##### No Longer With Us
Re: present perfect passive v. simple past passive.

There's no reason to change the original sentence.

#### hhtt21

##### Key Member
Re: present perfect passive v. simple past passive.

But in both cases ie the present perfect or past simple, we are searching for the speed, the maximum speed just before the brakes. The brakes are applied. At that time, both brakes are applied and the car has its maximum speed and this is the time the skid marks beginning to form. What is wrong with this explanation?

Thank you.

#### GoesStation

##### No Longer With Us
Re: present perfect passive v. simple past passive.

Original: How can we use the skid marks of a car to estimate the car's speed before the brakes were applied."

<snip>

How can we use the skid marks of a car to estimate the car's speed before the brakes have been applied."

But in both cases ie the present perfect or past simple, we are searching for the speed, the maximum speed just before the brakes. The brakes are applied. At that time, both brakes are applied and the car has its maximum speed and this is the time the skid marks beginning to form. What is wrong with this explanation?
Your version is illogical. The car will produce skid marks after the brakes are applied. Since the skid marks are not there yet, you can't use them to estimate anything before the brakes have been applied.

#### hhtt21

##### Key Member
Re: present perfect passive v. simple past passive.

Your version is illogical. The car will produce skid marks after the brakes are applied. Since the skid marks are not there yet, you can't use them to estimate anything before the brakes have been applied.
If "before the brakes have been applied" is used the marks do not appear but if "before the brakes were applied" is used the marks appear. This is the point I cannot distinguish the difference and I do not know how I will distinguish. I cannot distinguish how this two tenses introduce very different situations.

So, would you please try to explain this "distinguishing point" in a different way?

Thank you.

#### GoesStation

##### No Longer With Us
Re: present perfect passive v. simple past passive.

I understand your confusion. I hope one of our actual teachers can jump in here to explain this. I'm sorry, but I don't know how.

#### jutfrank

##### VIP Member
Re: present perfect passive v. simple past passive.

I believe that the cause of the confusion here may be to do with ways of seeing the context. I can see two ways of understanding this example:

1) We are talking about a case in hypothetical past time. (I believe this is how GoesStation is seeing it.) We assume that there was a specific incident, whether real or just hypothetical. In this case, were applied is better.

2) We are talking about a case in hypothetical general time. (Maybe this is how hhtt21 is seeing it.) We are talking purely hypothetically. In this case, have been applied is better. You could also use are applied.

It may be helpful to see this if the sentence is rephrased slightly:

How do you use skid marks to estimate the speed that a car is travelling at before the brakes have been applied?

As the example comes from a maths textbook, it could be either.

Does that make sense? Please tell me if I'm wrong.

#### hhtt21

##### Key Member
Re: present perfect passive v. simple past passive.

I believe that the cause of the confusion here may be to do with ways of seeing the context. I can see two ways of understanding this example:

1) We are talking about a case in hypothetical past time. (I believe this is how GoesStation is seeing it.) We assume that there was a specific incident, whether real or just hypothetical. In this case, were applied is better.

2) We are talking about a case in hypothetical general time. (Maybe this is how hhtt21 is seeing it.) We are talking purely hypothetically. In this case, have been applied is better. You could also use are applied.

It may be helpful to see this if the sentence is rephrased slightly:

How do you use skid marks to estimate the speed that a car is travelling at before the brakes have been applied?

As the example comes from a maths textbook, it could be either.

Does that make sense? Please tell me if I'm wrong.

You catch the point. But because can is used "how can we use the skid marks ..." does not this imply a general case? Would you please explain why "have been applied" is better? Is it because of there is a very small time interval between applying brakes and the skidding process?

Thank you.

#### hhtt21

##### Key Member
Re: present perfect passive v. simple past passive.

The preset perfect in the original post is natural and correct. You might say that it is also logical. This sentence could easily be found in any instruction manual or on a test. It is not necessary that the event has occurred. It may be hypothetical.

No, it is not the present perfect in the original but simple past and this is what is confusing for me. I have confusions that the author are native speakers. I have some situations such that before. The natives speakers did not like textbooks whose sentences I asked about. Even they were well-known textbooks and had 7th or 8th edition but nothing was corrected for language. Are the surnames Keedy and Bittinger American? This can be a hint for whether or not they are native speakers. See #1.

Thank you.

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#### jutfrank

##### VIP Member
Re: present perfect passive v. simple past passive.

It's conceivable that the writers were thinking of past time (case 1 in post #11). I don't know, but I assume they are native-speakers. Either way, I don't think the sentence is written as well as it could have been.

If speaking purely hypothetically (case 2 in post #11), I think are applied is better than have been applied, actually, though both are fine. were applied is not appropriate.

Using can does not necessarily imply a general case, no. The contrary if anything.

#### andrewg927

##### Senior Member
Re: present perfect passive v. simple past passive.

I can see that the confusion is only building up with conflicting information. Honestly, I think the original sentence is perfect. "were" sounds more natural because you can't have skid marks until the brakes have been applied. I don't find "are" sounds any better at all. I agree with Robert that "before the brakes have been applied" is acceptable (meaning it is not wrong) but I don't prefer it. Using last names to guess if the person is a native speaker is based on the false premise that unless the last name sounds Anglophone the person is not a native English speaker.

Another thing, hhtt21, natives speakers may not like the things you ask in your English books possibly because they can be confusing even to a native speaker. English teachers tend to write things in black and white possibly because they think that would be easier for non-native speakers to understand. I have no problem with you asking anything from your books but please understand the English language is not black and white and most native speakers are not language experts.

#### GoesStation

##### No Longer With Us
Re: present perfect passive v. simple past passive.

Are the surnames Keedy and Bittinger American?
America is inhabited by people from all over the world. The majority of the current population is of European heritage, especially Irish, English, Scottish, German, and Italian. We have a very large number of people whose families came from Latin America and usually have Spanish surnames, but we have large populations with Indian, Chinese, Japanese, and other types of names as well.

So you can see that there's no way to guess from an author's name whether they're American.

#### andrewg927

##### Senior Member
Re: present perfect passive v. simple past passive.

Indeed we have many with Spanish surnames like Garcia, Martinez, Rodriguez, to name a few. Even though not all of them are English native speakers, many of them are.