how to understand "have had to"

[cooper]

Sirs:
Here is example" Previously, patient with hearing impairment have had to rely on behind-the-ear hearing aid", So i am not sure what different is it if there is lack of first "have"

thanks for your attention

[David L.]

Look at these two sentences:
Last century, patients with hearing impairment had to rely on behind-the-ear hearing aids. Now, with the advent of WiFi computer technology, and a cranial implant.."
(Sounds painful!)

Till now, patients with hearing impairment have had to rely on behind-the-ear hearing aids. The new WIFI computer technology revolutionizes the way...

Can you see what the difference is, in terms of 'time', between the two?

[riverkid]

Look at these two sentences:
Last century, patients with hearing impairment had to rely on behind-the-ear hearing aids. Now, with the advent of WiFi computer technology, and a cranial implant.."
(Sounds painful!)

Till now, patients with hearing impairment have had to rely on behind-the-ear hearing aids. The new WIFI computer technology revolutionizes the way...

Can you see what the difference is, in terms of 'time', between the two?

There's a distinct difference in your examples, David, because of your choice of adverbials but the original works either with or without 'have'.

Previously, patients with hearing impairment have had to rely on behind-the-ear hearing aids", ...

Previously, patients with hearing impairment had to rely on behind-the-ear hearing aids", ...

[2006]

There's a distinct difference in your examples, David, because of your choice of adverbials but the original works either with or without 'have'.
Previously, patients with hearing impairment have had to rely on behind-the-ear hearing aids", ...

Previously, patients with hearing impairment had to rely on behind-the-ear hearing aids", ...

Actually, David's examples also work without "have".
cooper: In your sentence, there is no difference without "have".

[cooper]

first of all let me say Thanks
In David's example,what I understand on 2'nd sentence is hearing-impaired people now still have to rely on behind-the-ear device.
So in my sentence,the time is set in the past, "have" should be cutted off. I don't understand.

[2006]

first of all let me say Thanks
In David's example,what I understand on 2'nd sentence is hearing-impaired people now still have to rely on behind-the-ear device. That's not the way I understand it. (Till) (Until) means 'before'.
1...Till now they had to rely on...., but they don't have to rely on...any more.
2...If they still have to rely on..., it should just say, 'Now patients with hearing impairment have to rely on...'.
So in my sentence,the time is set in the past, "have" should be cutted off. I don't understand.

2006

[cooper]

got it,(Till) (Until) means 'before'

[2006]

got it,(Till) (Until) means 'before'

Yes, that's what it means to me.
The other thing that I should have mentioned is that the sentence "The new WIFI computer technology...." further tells us that the situation has changed and that those patients no longer have to rely on.... So, that again tells us that "Till now" refers to the past and therefore 'had' is all we need; we don't need "have had".

[David L.]

Good. I'm glad you gave it a go. I wanted to try to grasp how you might see the difference.

Last century, patients with hearing impairment had to rely on behind-the-ear hearing aids. Now, with the advent of WiFi computer technology, and a cranial implant..."

Till now, patients with hearing impairment have had to rely on behind-the-ear hearing aids. The new WIFI computer technology revolutionizes the way...

In the first sentence, using the Simple Past Tense, there is a simple contrast between 'then' (last century) and 'now'. It is like two single points in time - yesterday that happened, today this happens - we are not concerned with any span of time.

In the second sentence, I used the time expression 'till now' so that you can immediately grasp that here, we are referring to a span of time, from some unspecified moment in the past (perhaps when hearing aids were first invented), over all the years up to this moment.
We use the Present Perfect Tense for actions started in the past and continuing in/ or up to the present.
What's the difference in terms of why use one tense or the other?
In the first, the speaker is making a simple contrast between the technology available then, versus now.
In the second, I am emphasizing that throughout the whole history of hearing aids, poor patients have had only the behind-the -ears model, whereas, now and from this moment on, their lives are radically changed because of this new revolutionary...
Let's go back to your original sentences:
1. "Previously, patients with hearing impairment had to rely on behind-the-ear hearing aids."
2. " Previously, patients with hearing impairment have had to rely on behind-the-ear hearing aids."
The sentence opens with the time reference 'previously'. This could refer to a single moment in time before now, or a span of time up to now. e.g.
"We retract...Mr. Paul Smith did not murder his wife, as previously stated, (simple past tense) - it was his brother, Tom Smith."
"The girls are enrolled in the Browning School. Previously, they had been attending..." (past perfect because of the span of time involved in 'attending a school')
So we come to the heart of this matter : the choice of tense reflects the person's subjective view of the situation, and the time frame. That is why both sentences you quote are possible, and so it depends on the speaker what aspect he wishes to emphasize. Does he want to just say, that was then, this is now, and just look at this new technology.

Or...is, to his mind, how things have changed for patients over time - (all those years of just having old-fashioned behind-the-ear devices) - just as important as talking about this new model that's come on the market. It is almost as if he is referring to the relief that this change will bring to patients who have had to put up with with old technology! 'All those years of making do with primitive technology - but now, help has arrived!'

Now, if anything still isn't clear, post again.

[riverkid]

Good. I'm glad you gave it a go. I wanted to try to grasp how you might see the difference.

Last century, patients with hearing impairment had to rely on behind-the-ear hearing aids. Now, with the advent of WiFi computer technology, and a cranial implant..."

Till now, patients with hearing impairment have had to rely on behind-the-ear hearing aids. The new WIFI computer technology revolutionizes the way...

In the first sentence, using the Simple Past Tense, there is a simple contrast between 'then' (last century) and 'now'. It is like two single points in time - yesterday that happened, today this happens - we are not concerned with any span of time.

In the second sentence, I used the time expression 'till now' so that you can immediately grasp that here, we are referring to a span of time, from some unspecified moment in the past (perhaps when hearing aids were first invented), over all the years up to this moment.

We use the Present Perfect Tense for actions started in the past and continuing in/ or up to the present.

What's the difference in terms of why use one tense or the other?
In the first, the speaker is making a simple contrast between the technology available then, versus now.
In the second, I am emphasizing that throughout the whole history of hearing aids, poor patients have had only the behind-the -ears model, whereas, now and from this moment on, their lives are radically changed because of this new revolutionary...
Let's go back to your original sentences:
1. "Previously, patients with hearing impairment had to rely on behind-the-ear hearing aids."
2. " Previously, patients with hearing impairment have had to rely on behind-the-ear hearing aids."
The sentence opens with the time reference 'previously'. This could refer to a single moment in time before now, or a span of time up to now. e.g.
"We retract...Mr. Paul Smith did not murder his wife, as previously stated, (simple past tense) - it was his brother, Tom Smith."
"The girls are enrolled in the Browning School. Previously, they had been attending..." (past perfect because of the span of time involved in 'attending a school')
So we come to the heart of this matter : the choice of tense reflects the person's subjective view of the situation, and the time frame. That is why both sentences you quote are possible, and so it depends on the speaker what aspect he wishes to emphasize. Does he want to just say, that was then, this is now, and just look at this new technology.

Or...is, to his mind, how things have changed for patients over time - (all those years of just having old-fashioned behind-the-ear devices) - just as important as talking about this new model that's come on the market. It is almost as if he is referring to the relief that this change will bring to patients who have had to put up with with old technology! 'All those years of making do with primitive technology - but now, help has arrived!'

Now, if anything still isn't clear, post again.

An excellent overview, David. I'll just add a couple of comments, in blue, to something you wrote.

David wrote:
"We sometimes use the Present Perfect for actions started in the past and continuing in/ or up to the present."

The Present Perfect also describes finished actions that we want to make current or add importance to.

The prime minister has been shot.