What Makes Demand Elastic or Inelastic

Four things push elasticity up or down. Substitutes matter most: the more close substitutes a good has, the easier it is to walk away from a price hike, so demand gets more elastic. That's why Coke is elastic (switch to Pepsi) but soda in general is inelastic (what else fills that role?). Necessity cuts the other way: insulin has almost no substitutes and no optional use, so its demand is steeply inelastic no matter the price. Budget share matters too: a good that eats a small slice of income, like salt, barely changes behavior when its price doubles, because the dollar amount is trivial either way. A good that eats a big slice, like rent or a laptop, makes buyers much more price-sensitive.

Time is the sneaky one. The same good can be inelastic today and elastic in five years, because elasticity depends on how many substitutes you can act on, and that number grows as time passes. Gas this week is inelastic: you still have to drive to work tomorrow. Gas over a decade is elastic: you can buy a hybrid, move closer to work, or take transit. Short-run demand curves are steep; long-run demand curves for the same good are flatter.

This sets up the next step: once you know what makes demand bend more or less, you can predict who absorbs a tax or price floor, since the less elastic side of a market always bears more of the burden.