It is often said that you cannot compare apples and oranges. You can. Sometimes, you must.
The confusion comes from failing to distinguish between the items being compared[1] and the basis of comparison.
For example, it is perfectly legitimate to compare the following between apples and oranges:
- Vitamin C content per 100g
- Price per item in Tesco
- Time taken to ripen
However, it is not meaningful (unless additional criteria are defined) to compare:
- The crunchiness of one apple against the taste of another
- The vitamin C content of one apple vs the colour of another
The conflict is not between the classes of object being compared but the class of comparison being made[2][3].
[1] A number of apples cannot be considered inherently equivalent to some other number of oranges, unless there is an agreed additional basis of comparison (eg vitamin C content per 100g. Such agreed basis of comparison may be termed a Value Metric. The Value Metric is general the result of some social negotiation. The negotiation is not always entirely rational – see Mornington Crescent theory of Management.
[2] See also Category Mistake, Gilbert Ryle- https://en.wikipedia.org/wiki/Category_mistake
[3] In many cases, things can be compared if they have the same units, but not necessarily. Work and torque both have units of kg.m2.s-2 , but one is a scalar and the other is a pseudovector (antisymmetric 2nd rank tensor) and they are not meaningful to compare.