Well, if you mean "a group of people conspiring to do something" then yes, cospiracies do take place. And yes, governments and large agencies do try and keep secrets from the people. We know this because they usually get caught out, the main reason being that, the more people involved in keeping a secret (and when it comes to large organisations with large secrets, the numbers involved are going to be correspondingly large) the more likely it is that someone will leak information.markfiend wrote:Labelling an idea "conspiracy theory" doesn't automatically mean that the idea is false; Raf's Wiki link mentions several real conspiracies that are historically documented.
But few if any of the so-called proven conspiracies really correspond to the more outlandish sorts of things usually associated with conspiracy theories such as harbouring aliens, assassinating Kennedy or - Lord have mercy - faking the moon landings. That particularly hilarious notion was finally comclusively debunked by, of all people, Neil Morrissey on TV some years ago where, after disproving all the other elements, they dealt with the stickiest issue - the photos with supposedly impossible light sources - by recreating the conditions and taking matching photos.
Now, you'll have to excuse me - the police are asking awkard questions about the yeti in my spare room.