Can you return an instant card from the graveyard to your hand using Regrowth?

Regrowth (from Alpha through its many reprintings) reads: 'Return target card from your graveyard to your hand.' Because the text specifies only 'card' and places no restriction on card type, any card legally in your graveyard is a valid target — including instant cards.

Under CR 109.2, a 'card' refers to a Magic card. Since instants are cards (CR 304.1), they satisfy the targeting requirement with no additional conditions needed.

The graveyard is a public zone (CR 403.1), and cards in it retain their types and characteristics (CR 400.7), so the game always knows a card is an instant even while it sits in the graveyard. Regrowth simply reads those characteristics to confirm the target is 'a card,' which an instant certainly is.

Concrete example: You cast Lightning Bolt, which resolves and goes to your graveyard. On your next turn you cast Regrowth, targeting Lightning Bolt in your graveyard. Regrowth resolves, and Lightning Bolt returns to your hand, ready to be cast again.

There are no timing tricks here — Regrowth itself is a sorcery, so you cast it during your main phase, but the instant you retrieve can of course be cast at instant speed once it's back in your hand (CR 304.1).