'different' vs 'differential' pricing (adjectives)

I'm not asking about them as nouns, or the calculus and mechanic meanings of 'differential'. ODO doesn't distinguish them, and synonymizes 'differential' with 'difference'.

1. In 1 beneath, why not use 'different'? What'd change?

2. Why not use 'differential'?

_{Source: The European Union: A Beginner's Guide. p. 139 Bottom - p. 140 Top. I, and not the book, bolded.}

Gender has traditionally played a key role in the pricing of insurance policies.
  In 2004 an EU Directive prohibited all discrimination based on sex in the access to a supply of goods or services. In principle the Directive therefore prohibited the use of gender as a method of determining insurance premiums and benefits with regard to contracts that were entered into after 21 December 2007. However, the Directive also stated [1.] differential pricing could be maintained where statistical evidence supported such an approach. Insurance companies regarded this as crucial because as women drivers are statistically proven to have fewer accidents than male drivers, premiums for female insurance policies have generally been lower. In a similar way, because women live longer, men have traditionally received a higher rate from their pension annuities because their life expectancy is lower and as such their pension savings are able to produce more income over a shorter time.
  Such continued practice of price differentials was subject to a review after the Belgian Constitutional Court asked the European Court of Justice to assess the validity of differential pricing. This in turn resulted in the ECJ ruling on 1 March 2011 that insurers cannot charge [2.] different premiums to men and women based on their gender from 21 December 2012 onwards. In the case of car insurance, the significance of this ruling is that female car insurance premiums will rise while male insurance premiums will fall. And where high costs of insurance have in the past discouraged young men from buying fast cars that are more likely to lead to road accidents, a reduction in insurance costs could worryingly result in greater purchases of high performance cars.

Solution 1:

I think there are lots of cases where either "differential" or "different" would be acceptable. However, there is a difference in usage between the words. Compare the entries in MW for "differential"

1a. of, relating to, or constituting a difference

1b. making a distinction between individuals or classes

and "different".

1. partly or totally unlike in nature, form, or quality
2. not the same

"Differential pricing" doesn't just mean "different pricing"; it means that the pricing system is different for different classes of people (in this case, men and women). The same product is being sold to different groups for different prices. Pricing is being used to distinguish two classes.

"Different premiums" however does work, because of the way it's used: "insurers cannot charge different premiums to men and women." I think that could be reworded to be "insurers cannot charge differential premiums based on sex." But saying "insurers cannot charge differential premiums to men and women" would probably sound awkward.

Also, aside from the dictionary definitions, "differential" is commonly used in a lot of technical jargon where "difference" or "different" wouldn't work. "Differential equations", "differential steering", and "differential pricing" cannot be replaced with "different equations" etc. In these cases, "differential" describes a system that relies on or is related to differences; it doesn't just mean "different".

Solution 2:

Different prices (or premiums as in the example) means prices (premiums) that are not the same.

Differential pricing uses the present participle and gives the phrase an active verbal feeling, i.e. it is the process or activity of setting different prices. It also has a technical definition as a commenter above commented, so should probably be used accordingly to avoid ambiguity.

Definition from business jargons: The Differential Pricing is a method of charging different prices for the same type of a product, and for the same number of quantities from different customers based on the product form, payment terms, time of delivery, customer segment, etc.

Solution 3:

The technical phrase "differential pricing" avoids the ambiguity that comes with just using the word "different." Differential pricing refers to the practice of maintaining different prices, or the state of affairs that results from that practice. Different pricing could refer to a lot of things.

1. "However, the Directive also stated differential pricing could be maintained where statistical evidence supported such an approach."

"Different pricing" would be ambiguous in this sentence. It could refer to a completely different pricing scheme, rather than a pricing scheme where certain customers are charged different prices than other customers. (i.e. If I switch from a differential pricing scheme to a non-differential pricing scheme, I'm using a different pricing scheme.)

2. This in turn resulted in the ECJ ruling on 1 March 2011 that insurers cannot charge different premiums to men and women based on their gender from 21 December 2012 onwards.

You could use "differential" here, but it is unnecessary. "Different" in this sentence refers to the premiums charged to individuals, rather than the pricing scheme applied to the population.