In Magic: The Gathering, are enchantments and artifacts considered spells?
More precisely, can I use Cancel (which says "Counter target spell.") on an enchantment or an artifact?
Since you asked for some citations from the official rules:
So basically, pretty much every card in Magic is a "spell" - or rather, becomes one, during the transitional period from being a card in your hand to being a permanent on the battlefield. But wait! Why isn't a land a spell, in that case? Well, because it has special rules making it an exceptional case:
The Magic rules are pretty arcane at the best of times (appropriately enough), but I hope that clarifies things for you!
EDIT: Actually, it occurs to me that even more clarification may be necessary. Enchantments and artifacts aren't spells when they're in play: they're permanents. They aren't spells when they're in their hand, they're enchantment cards and artifact cards. But they are spells while on the stack (i.e. in the process of being cast). I'm sure you already know that "counter target spell" means "stop something on the stack from resolving and becoming a permanent, and send the card to the graveyard instead", but it wasn't 100% explicit from your question! So, just in case there's any doubt at all, Cancel can stop an artifact or enchantment card from coming into play, but it can't send it to the graveyard from play, or anything wacky like that...
A "spell" refers to a card while it's on the stack. In order:
While it's in your hand, it's a card (enchantment card, creature card, land card) While you're casting it and it's on the stack, it's a spell. (creature spell, enchantment spell, etc.) Once it's resolved, if it stays in play it's a permanent. (Instants and sorceries just resolve and discard.)
Lands are the exception - they don't use the stack and go directly from card to permanent.
Yes. Of all the card types, the only one that isn't a spell are lands. "Counter target spell" can counter sorceries, instants, enchantments, artifacts, creatures, and planeswalkers.
Tribal is also a card type, but it always shows up in conjunction with one of the other types, so it doesn't matter in this case.