Searching Library vs choosing a card

[wox2]

I know that I am able to not find a card during searching the library that is specific(nonland, Island, sorcery...). 1) What about Demonic tutor and looking for card? Do I have to search card?

2) And what about Thoughseize? If I see my opponents cards with maddness do I have to discard them? Or if my thoughtseize is Missdirected?

[Anusien]

Search: If you're required to search a zone not revealed to all players for cards of a given quality, such as card type or color, you aren't required to find some or all of those cards even if they're present; however, if you do choose to find cards, you must reveal those cards to all players. Even if you don't find any cards, you are still considered to have searched the zone. If you're simply searching for a quantity of cards, such as "a card" or "three cards," you must find that many cards (or as many as possible). These cards often aren't revealed.

Any effect that says "Choose" you cannot fail on as long as there is a legal choice.  So if you Duress the opponent and his only card is Bridge from Below, you have to choose it.

[Nefarias]

To answer the questions you're asking, you have to chose something with Thoughtseize if there is a legal card (aka a non-land). If it gets Misdirected to you, again you must choose something. The distinction here is that Thoughtseize reveals the hand, making it public information, and therefore all players are able to discern whether or not there is a legal choice.

I am fairly certain that you do have to find a card with Demonic and Vampiric Tutors though. While the actual contents of the library are not public information, it is public information that there is at least a card in the library, and hence all players can discern that there must be a legal choice.

I remember a rules-lawyering situation regarding this. During a high-REL event, a player cast Vampiric Tutor, put it in his graveyard, and then began to search. His opponent called the judge over, and tried to argue that by putting the card in the graveyard (the final action of resolution), its caster implied that the spell had fully resolved and had failed to find. The ruling was that while the player may have had a case if it had been Mystical Tutor, Vampiric cannot fail to find, as there are clearly legal choices.

And just to compound upon what Anusien was saying, take for example Guided Passage:

Guided Passage
URG
Sorcery
Reveal the cards in your library. An opponent chooses from among them a creature card, a land card, and a noncreature, nonland card. You put the chosen cards into your hand. Then shuffle your library.

If this were worded as "An opponent searches your library for...." the card would do nothing as the opponent could just fail to find. But since it reveals (again, making it public info), and uses the word "chooses," they must make legal choices if there are any available.

[Godder]

I am fairly certain that you do have to find a card with Demonic and Vampiric Tutors though. While the actual contents of the library are not public information, it is public information that there is at least a card in the library, and hence all players can discern that there must be a legal choice.

This is still true - Intuition, Vamp, DT and Grim Tutor are all commonly played cards in Eternal MTG that require a card(s) to be found if a search is made.

[Clariax]

To answer the questions you're asking, you have to chose something with Thoughtseize if there is a legal card (aka a non-land). If it gets Misdirected to you, again you must choose something. The distinction here is that Thoughtseize reveals the hand, making it public information, and therefore all players are able to discern whether or not there is a legal choice.

The distinction is that there is no search happening with Thoughtseize.  The rules concerning failing to find when searching are specific to searching.  If the effect doesn't specify a search, it's not a search, regardless of how similar it may seem.  The effect simply tells you to make a choice, so you must make a choice (if able).  Not making a choice isn't an option.  The fail to find rule also does specify that it's only if the zone is not revealed to all players, but again, applies only to a "search," which thoughtseize is not.

[andrewpate]

So just to clarify, searching is like targeting:  there are special rules for it, and anything not explicitly using the word does not abide by those rules.  So in the same way a card that said, "Choose a creature.  Deal 3 damage to that creature," could hit a creature with shroud despite functioning more or less just like a Lightning Bolt, a card that seems to search but does not have the word "search" in its text box does not actually search.

Is this what you were trying to say, Clariax?

[Clariax]

So just to clarify, searching is like targeting:  there are special rules for it, and anything not explicitly using the word does not abide by those rules.  So in the same way a card that said, "Choose a creature.  Deal 3 damage to that creature," could hit a creature with shroud despite functioning more or less just like a Lightning Bolt, a card that seems to search but does not have the word "search" in its text box does not actually search.

Is this what you were trying to say, Clariax?

Search, target, draw, discard, etc.  There's many words in magic which have special rules meaning.  An effect may move a card from your library to your hand (Fact or Fiction for example) without being a draw event.  Just like something may tell you to choose something in a specific zone without searching or targetting.