<p><strong>Demand is a function</strong></p>
<p>In economics, &quot;demand&quot; is an unfortunate shorthand for &quot;demand function&quot;. Less frequently and even more unfortunately it is also used for quantity demanded at the current price. Many textbooks make the effort to use &quot;demand schedule&quot; instead of &quot;demand&quot;.</p>
<hr />
<p><strong>Functions and operators</strong></p>
<p>The <a href="https://en.wikipedia.org/wiki/Elasticity_of_a_function" rel="nofollow noreferrer">elasticity of function</a> <span class="math-container">$f$</span> is another function <span class="math-container">$\epsilon_f$</span> describing some aspect of the function <span class="math-container">$f$</span>.</p>
<p>The linguistic structure is similar to derivative of function <span class="math-container">$f$</span>.</p>
<hr />
<p><strong>Multivariate functions</strong></p>
<p>Why not just have &quot;elasticity of the demand function&quot; then, why put the word &quot;price&quot; in there? General demand functions have multiple variables, such as income or prices of other goods. Elasticity can also be calculated according to these variables, i.e. income elasticity and cross-price elasticity exists. Thus adding the word &quot;price&quot; is necessary.</p>
<hr />
<p><strong>Language</strong></p>
<p>One could indeed phrase it as &quot;elasticity of function <span class="math-container">$D_1$</span> with respect to <span class="math-container">$p_1$</span>&quot; instead of &quot;price elasticity of <span class="math-container">$D_1$</span>&quot;. This would make it sound more like partial derivative of <span class="math-container">$f$</span> w.r.t. <span class="math-container">$x_i$</span> or the bivariate ratio. But the second phrase is a bit shorter, well defined, and understood by most people who use it.</p>
<hr />
<p>Disclaimer: I am not a native English speaker.</p>

CC BY-SA 4.0
2021-08-08T19:07:08.417Z
There is something here that goes beyond mere English, as in your observation "The linguistic structure is similar to derivative of function $f$."  Something as simple as "Demand Elasticity of Price" would bring to mind "DemandElasticity(price)" reifying something called "Demand Elasticity" which, itself, would bring to mind physical analogs such a "Rubber Elasticity" with which people are familiar by analogy.  But such a reversal is definitely off the table.  However, how about "Pricing Elasticity of Demand"?  The "ing" indicates a changing stimulus.
James Bowery
CC BY-SA 4.0
2021-08-08T05:04:13.537Z
2021-08-08T05:43:46.793Z
2021-08-08T05:43:46.793Z
Giskard
<blockquote>
<p>What is the proper way to read and/or express “price elasticity of demand”?</p>
</blockquote>
<p>Price elasticity of demand is for simple demand function defined as following:</p>
<p><span class="math-container">$$EL_D = \frac{\partial Q(p)}{\partial p} \frac{p}{Q(p)}$$</span></p>
<p>so the price elasticity of demand is a product of a slope of a demand function evaluated at some specific price and a ratio of that price to the demand function evaluated at the said price. The elasticity express by how much quantity demanded changes (in % terms) when price changes by <span class="math-container">$x\%$</span>.</p>
<p>Also,</p>
<blockquote>
<p>So this leads one to interpret &quot;price elasticity of demand&quot; as a change in demand resulting in a change in something called &quot;price elasticity&quot;.</p>
</blockquote>
<p>This is purely subjective, I think &quot;price elasticity of demand&quot; leads one to interpret the sentence as response/stretching of demand as a result of change in price which is exactly what it describes.</p>
<blockquote>
<p>Lest people think I'm being just a mite too persnickety about all this natural language stuff, there does seem to be a major gap between the economics profession and even the college educated public affected by economic policy, resulting in what might charitably be called &quot;an impedance mismatch&quot;</p>
</blockquote>
<p>I don't think this makes much sense:</p>
<ol>
<li><p>I don't see any evidence for some widespread confusion about the term, I teach economics to undergraduates and I rarely see students having problem grasping the concept. I never seen any data or had experience of some general confusion about the  concept of elasticity in particular.</p>
</li>
<li><p>Even if we would grant the premise that the name price elasticity of demand is somehow causing confusion among laymen, this confusion can be in present day cleared instantly by just googling the term. I can imagine that avoiding &quot;an impedance mismatch&quot; could have some utility in and prior to 20th century, but not much now.</p>
</li>
<li><p>I can't possibly see how &quot;bivariate function ratio&quot; would be more natural or less confusing to layman. It is not even accurate since elasticity can be function of multiple variables in principle. Following, EMFE by Hammond et al pp 407. the general formula for elasticity is given by:</p>
</li>
</ol>
<p><span class="math-container">$$EL_i z = \frac{x_i}{f(\mathbf{x})}\frac{\partial f(\mathbf{x})}{\partial x_i}$$</span></p>
<p>where <span class="math-container">$\mathbf{x}$</span> can be arbitrary large vector.  So calling it &quot;bivariate function ratio&quot; is not even accurate. If you want to be accurate an elasticity is &quot;a product of a slope of a function evaluated at some specific input with a ratio of input to function evaluated at the said input holding all other inputs constant.&quot; However, not only is that mouthful I doubt for regular person that would be more clear description.</p>
<ol start="4">
<li><p>In virtually all fields of science there are words/jargon that is not completely natural. When a layman person hears words like &quot;rational number&quot; or &quot;irrational number&quot; they often make association with rationality in a sense of 'being smart' rather than the fact that rational refers to an ability of the number to be expressed as a ratio/fraction of two integers. So would it make sense to now go and relabel these ratio and non-ratio numbers, just because it would have more 'natural'/easier interpretation for laymen?</p>
<p>I think not. Not only would that yield very little benefit in present day where the correct definition can be easily obtained, it would make it harder to relate any mathematical text written before this change to new texts. In the end people would have to learn both definitions just for the sake of continuity. Equivalently, in economics people would still have to learn what elasticity of demand means even if we would suddenly decide to switch to new terminology, because of the continuity in economics research and people working on new ideas often have to cite old work, sometimes even decades old. This would just create more trouble than it is worth. It is no accident that in all branches of science terminology is rarely 'updated', with many branches of science even using Latin terms long after using Latin-based terminology makes any sense.</p>
</li>
</ol>

CC BY-SA 4.0
2021-08-08T20:48:15.197Z
As pointed out by Giskard, elasticity is really a functional, like partial derivative.  Given your emphasis on the multivariate nature of elasticity (in which "demand" isn't just another so much as the functional) the phrase "partial elasticity" therefore seems appropriate and would lend itself to "price partial elasticity of demand" which would reach across disciplines quite effectively while being more accurate even within the discipline of economics.  Adopting this cross-discipline-friendly phrase suggests "total elasticity" analogous to "total derivative".  But that's for another question.
James Bowery
CC BY-SA 4.0
2021-08-08T20:50:07.747Z
@JamesBowery but elasticity is not analogous to total derivative, also terminology partial price elasticity of demand is used, but usually people abbreviate
1muflon1
CC BY-SA 4.0
2021-08-08T20:59:56.447Z
But elasticity _is_ analogous to _partial_ derivative.  I only bring up the notion of "total" derivative as analogous to something that _may_ be of interest to the field of economics.

https://math.stackexchange.com/a/1610797/11347
James Bowery
CC BY-SA 4.0
2021-08-08T00:03:39.380Z
2021-08-08T00:17:19.883Z
2021-08-08T00:17:19.883Z
1muflon1
<p>The natural language phrase such as <em>square root of x</em> for a function <span class="math-container">$Sqrt(x)$</span> precedes the input with the word <strong>of</strong>.   When we talk of a bivariate function, such as <span class="math-container">$x/y$</span> aka <span class="math-container">$Ratio(x,y)$</span>, we say simply <em>x divided by y</em> or, possibly <em>ratio <strong>of</strong> x <strong>to</strong> y</em>.</p>
<p>So, the phrase, <em>price elasticity <strong>of</strong> demand</em> would imply, not a bivariate function, but a function <span class="math-container">$PriceElasticity(demand)$</span>.</p>
<p>Moreover, when we speak of <em>causation</em> in mathematical models, we usually, likewise, speak in terms of the future being a function <strong>of</strong> the past.  Therefore, the thing named by the function is the effect; the response of the model.  The input to the function is the stimulus.</p>
<p>So this leads one to interpret &quot;price elasticity of demand&quot; as a change in demand resulting in a change in something called &quot;price elasticity&quot;.</p>
<p>Lest people think I'm being just a mite too persnickety about all this natural language stuff, there does seem to be a major gap between the economics profession and even the college educated public affected by economic policy, resulting in what might charitably be called &quot;an impedance mismatch&quot;.</p>
<p>After looking into this a bit, and discovering that the economists' &quot;elasticity&quot; has little to do with the long history of the word in <a href="https://www.worldscientific.com/worldscibooks/10.1142/7313" rel="nofollow noreferrer">mathematical physics</a>, I'm wondering if something more along the lines of the bivariate function <em>ratio</em> might better serve both the public and the economics profession.</p>
<p>Or am I simply displaying ignorance of the concepts behind &quot;elasticity&quot; as used in economics?</p>

<elasticity><soft-question><economic-terms>
What is the proper way to read and/or express "price elasticity of demand"?
James Bowery
# What is the proper way to read and/or express "price elasticity of demand"?

(Asked by: username_0 on 2021-08-07)

The natural language phrase such as *square root of x* for a function $Sqrt(x)$ precedes the input with the word **of**. When we talk of a bivariate function, such as $x/y$ aka $Ratio(x,y)$, we say simply *x divided by y* or, possibly *ratio **of** x **to** y*.

So, the phrase, *price elasticity **of** demand* would imply, not a bivariate function, but a function $PriceElasticity(demand)$.

Moreover, when we speak of *causation* in mathematical models, we usually, likewise, speak in terms of the future being a function **of** the past. Therefore, the thing named by the function is the effect; the response of the model. The input to the function is the stimulus.

So this leads one to interpret "price elasticity of demand" as a change in demand resulting in a change in something called "price elasticity".

Lest people think I'm being just a mite too persnickety about all this natural language stuff, there does seem to be a major gap between the economics profession and even the college educated public affected by economic policy, resulting in what might charitably be called "an impedance mismatch".

After looking into this a bit, and discovering that the economists' "elasticity" has little to do with the long history of the word in [mathematical physics](https://www.worldscientific.com/worldscibooks/10.1142/7313), I'm wondering if something more along the lines of the bivariate function *ratio* might better serve both the public and the economics profession.

Or am I simply displaying ignorance of the concepts behind "elasticity" as used in economics?

**Tags:** elasticity, soft-question, economic-terms

---

## 2 answers

### Answer by username_1 on 2021-08-08. Score: 1 | Accepted answer

**Demand is a function**

In economics, "demand" is an unfortunate shorthand for "demand function". Less frequently and even more unfortunately it is also used for quantity demanded at the current price. Many textbooks make the effort to use "demand schedule" instead of "demand".

---

**Functions and operators**

The [elasticity of function](https://en.wikipedia.org/wiki/Elasticity_of_a_function) $f$ is another function $\epsilon\_f$ describing some aspect of the function $f$.

The linguistic structure is similar to derivative of function $f$.

---

**Multivariate functions**

Why not just have "elasticity of the demand function" then, why put the word "price" in there? General demand functions have multiple variables, such as income or prices of other goods. Elasticity can also be calculated according to these variables, i.e. income elasticity and cross-price elasticity exists. Thus adding the word "price" is necessary.

---

**Language**

One could indeed phrase it as "elasticity of function $D\_1$ with respect to $p\_1$" instead of "price elasticity of $D\_1$". This would make it sound more like partial derivative of $f$ w.r.t. $x\_i$ or the bivariate ratio. But the second phrase is a bit shorter, well defined, and understood by most people who use it.

---

Disclaimer: I am not a native English speaker.

> **Comments:**
> **username_0**: There is something here that goes beyond mere English, as in your observation "The linguistic structure is similar to derivative of function $f$."  Something as simple as "Demand Elasticity of Price" would bring to mind "DemandElasticity(price)" reifying something called "Demand Elasticity" which, itself, would bring to mind physical analogs such a "Rubber Elasticity" with which people are familiar by analogy.  But such a reversal is definitely off the table.  However, how about "Pricing Elasticity of Demand"?  The "ing" indicates a changing stimulus.  

---

### Answer by username_2 on 2021-08-08. Score: 1

> What is the proper way to read and/or express “price elasticity of demand”?

Price elasticity of demand is for simple demand function defined as following:

$$EL\_D = \frac{\partial Q(p)}{\partial p} \frac{p}{Q(p)}$$

so the price elasticity of demand is a product of a slope of a demand function evaluated at some specific price and a ratio of that price to the demand function evaluated at the said price. The elasticity express by how much quantity demanded changes (in % terms) when price changes by $x\%$.

Also,

> So this leads one to interpret "price elasticity of demand" as a change in demand resulting in a change in something called "price elasticity".

This is purely subjective, I think "price elasticity of demand" leads one to interpret the sentence as response/stretching of demand as a result of change in price which is exactly what it describes.

> Lest people think I'm being just a mite too persnickety about all this natural language stuff, there does seem to be a major gap between the economics profession and even the college educated public affected by economic policy, resulting in what might charitably be called "an impedance mismatch"

I don't think this makes much sense:

1. I don't see any evidence for some widespread confusion about the term, I teach economics to undergraduates and I rarely see students having problem grasping the concept. I never seen any data or had experience of some general confusion about the concept of elasticity in particular.
2. Even if we would grant the premise that the name price elasticity of demand is somehow causing confusion among laymen, this confusion can be in present day cleared instantly by just googling the term. I can imagine that avoiding "an impedance mismatch" could have some utility in and prior to 20th century, but not much now.
3. I can't possibly see how "bivariate function ratio" would be more natural or less confusing to layman. It is not even accurate since elasticity can be function of multiple variables in principle. Following, EMFE by Hammond et al pp 407. the general formula for elasticity is given by:

$$EL\_i z = \frac{x\_i}{f(\mathbf{x})}\frac{\partial f(\mathbf{x})}{\partial x\_i}$$

where $\mathbf{x}$ can be arbitrary large vector. So calling it "bivariate function ratio" is not even accurate. If you want to be accurate an elasticity is "a product of a slope of a function evaluated at some specific input with a ratio of input to function evaluated at the said input holding all other inputs constant." However, not only is that mouthful I doubt for regular person that would be more clear description.

4. In virtually all fields of science there are words/jargon that is not completely natural. When a layman person hears words like "rational number" or "irrational number" they often make association with rationality in a sense of 'being smart' rather than the fact that rational refers to an ability of the number to be expressed as a ratio/fraction of two integers. So would it make sense to now go and relabel these ratio and non-ratio numbers, just because it would have more 'natural'/easier interpretation for laymen?

   I think not. Not only would that yield very little benefit in present day where the correct definition can be easily obtained, it would make it harder to relate any mathematical text written before this change to new texts. In the end people would have to learn both definitions just for the sake of continuity. Equivalently, in economics people would still have to learn what elasticity of demand means even if we would suddenly decide to switch to new terminology, because of the continuity in economics research and people working on new ideas often have to cite old work, sometimes even decades old. This would just create more trouble than it is worth. It is no accident that in all branches of science terminology is rarely 'updated', with many branches of science even using Latin terms long after using Latin-based terminology makes any sense.

> **Comments:**
> **username_0**: As pointed out by Giskard, elasticity is really a functional, like partial derivative.  Given your emphasis on the multivariate nature of elasticity (in which "demand" isn't just another so much as the functional) the phrase "partial elasticity" therefore seems appropriate and would lend itself to "price partial elasticity of demand" which would reach across disciplines quite effectively while being more accurate even within the discipline of economics.  Adopting this cross-discipline-friendly phrase suggests "total elasticity" analogous to "total derivative".  But that's for another question.  
> **username_2**: @JamesBowery but elasticity is not analogous to total derivative, also terminology partial price elasticity of demand is used, but usually people abbreviate  
> **username_0**: But elasticity _is_ analogous to _partial_ derivative.  I only bring up the notion of "total" derivative as analogous to something that _may_ be of interest to the field of economics.  https://math.stackexchange.com/a/1610797/11347  

---

