What is a perfect inelastic demand?

Answer 1

When demand for a product or service does not change at all in response to changes in its price. Of course in the real world that rarely if ever happens; it's an extreme case used to illustrate one endpoint of the spectrum of supply-and-demand responses by consumers.

Answer 2

If you're asking what a perfectly inelastic demand curve looks like, it's a perfectly vertical line.

If you're asking how it happens, it can happen for goods that are a necessity (something you can't live without and have to buy no matter how expensive it gets)

Answer 3

In economic theory, a perfect inelastic demand is a demand for some product that cannot be reduced, either by higher prices or shortages, because it is something that people absolutely have to have at any cost. There would be very few examples of a perfect inelastic demand. Some people need a certain kind of medicine to treat their disease, such as a severe diabetic who needs insulin; this is a perfectly inelastic demand. A heroin addict must have his or her heroin, regardless of cost, so that too is a perfectly inelastic demand. But most products have some elasticity of demand. If you cannot afford fruit juice, you can probably drink water instead.