Condition 1 - Also known as "cocked and locked," means a round is in the chamber, the hammer is cocked, and the manual thumb safety on the side of the frame is applied.
Condition 2 - A round is in the chamber and the hammer is down.
Condition 3 - The chamber is empty and hammer is down with a charged magazine in the gun.
People have added two additional states, Conditions 0 and 4, Condition 0 meaning a round is in the chamber, hammer cocked, and safety off, and Condition 4 referring to the condition in which the chamber is empty, hammer is down and no magazine is in the gun.
The mode of readiness preferred by the experts is Condition One. Generally speaking, Condition One offers the best balance of readiness and safety. Its biggest drawback is that it looks scary to people who don't understand the operation and safety features of the pistol.
Condition Two is problematic for several reasons, and is the source of more negligent discharges than the other conditions. When you rack the slide to chamber a round in the 1911, the hammer is cocked and the manual safety is off. There is no way to avoid this with the 1911 design. In order to lower the hammer, the trigger must be pulled and the hammer lowered slowly with the thumb onto the firing pin, the end of which is only a few millimeters away from the primer of a live round. Should the thumb slip, the hammer would drop and fire the gun. Not only would a round be launched in circumstances which would be at best embarrassing and possibly tragic, but also the thumb would be behind the slide as it cycled, resulting in serious injury to the hand. A second problem with this condition is that the true 1911A1 does not have a firing pin block and an impact on the hammer which is resting on the firing pin could conceivably cause the gun to go off, although actual instances of this are virtually nonexistent. Finally, in order to fire the gun, the hammer must be manually cocked, again with the thumb. In an emergency situation, this adds another opportunity for something to go wrong and slows the acquisition of the sight picture.
Condition Three adds a degree of "insurance" against an accidental discharge since there is no round in the chamber. To bring the gun into action from the holster, the pistol must be drawn and the slide racked as the pistol is brought to bear on the target. This draw is usually called "the Israeli draw" since it was taught by Israeli security and defense forces. Some of the real expert trainers can do an Israeli draw faster than most of us can do a simple draw, but for most of us, the Israeli draw adds a degree of complexity, an extra step, and an opening for mistakes in the process of getting the front sight onto the target.
You can visit Syd's excellent "The Sight 1911A1" at:
http://www.sightm1911.com.
Syd, many thanks for allowing me to use this.