This may be chiefly an ESL phenomenon, but confusion exists concerning the use of the adjective demandable.
My attention was drawn to the topic by this email:
I am an English teacher [from Turkmenistan]. I know English pretty well; however, I confuse the words “demanding” and “demandable.” Can you help me to distinguish those words? “He has a demandable character.” Or, “he has demanding character, or characteristics?”
The OED defines demandable as “That may be demanded or claimed.” Merriam-Webster defines it as “subject to being demanded.” Here are examples of the correct usage of demandable:
A bank at the time of levy was entitled under state law to set off against the balance in the delinquent taxpayer’s checking account only those debts owed to the bank by the taxpayer which were liquidated and demandable at the time of the levy.
But the BIR argued the tax debts have become “demandable… and collectible,” as [the debtor] has been ignoring a final assessment notice sent to him.
Judicial power includes the duty of courts of justice to settle actual controversies involving rights which are legally demandable and enforceable.
Errors with demandable occur when the word is used to mean demanding, desirable, or in demand.
Here are examples of misuse:
INCORRECT: My demandable father was never satisfied.
CORRECT : My demanding father was never satisfied.
A person who makes severe or difficult demands on others is said to be demanding. For example, one might have “a demanding employer,” “a demanding coach,” or “a demanding spouse.” One may also speak of such things as “a demanding profession” or “a demanding competition.”
INCORRECT: [A gift of] jewelry is the best way to impress your loved one because it is one of the most demandable and loved product of the girls.
CORRECT: [A gift of] jewelry is the best way to impress your loved one because it is one of the most wanted and loved product of girls.
The syntax is still awkward, but desirable or wanted fits the context better than demandable.
INCORRECT: Climate control system, effective air conditioner, powerful engine and many other features have made it one of the most demandable cars.
CORRECT : Climate control system, effective air conditioner, powerful engine and many other features have made it one of the cars most in demand.
Something or someone needed, wanted, or sought after is said to be “in demand.”
If your intended meaning is “difficult to please” or “difficult to accomplish,” use demanding.
If your intended meaning is “wanted” or “sought after,” use desirable or in demand (or wanted or sought after).
Save demandable for a context in which one party has the legal right to demand something from another.
It is wise, as this article says, to “Save demandable for a context in which one party has the legal right to demand something from another.” It would also be wise to use the word no more than twice per century, if that.