Can you cast a spell for its escape cost if the card is in a zone other than the graveyard?

Escape is a keyword ability that functions as an alternative cost, but it comes with a strict zone restriction: the card must be in your graveyard for you to cast it using the escape cost. This is explicitly stated in CR 702.156a, which defines escape as an ability that lets you cast the card from your graveyard by paying the escape cost instead of its mana cost.

Alternative costs in general (CR 118.9) allow you to pay a different cost than a spell's mana cost, but they do not override any other rules about where a spell may be cast from. Since escape specifically requires the card to be in the graveyard, attempting to use escape from your hand, exile, or any other zone is simply not a legal option.

If a card with escape ends up in your hand (say, via a draw or some other effect), you can still cast it normally for its mana cost — you simply cannot use the escape alternative cost in that situation.

Concrete example: Suppose you have Ox of Agonas in your hand. You may cast it for its normal mana cost of {2}{R}{R}, but you cannot cast it for its escape cost of {R}{R} plus exiling eight cards from your graveyard, because the card is not in your graveyard. Only once Ox of Agonas is in your graveyard may you cast it using escape.

In summary, the escape keyword is zone-locked to the graveyard by its own definition (CR 702.156a). No other zone qualifies, regardless of any other effects in play.