Depends on what you are asking. If you have a signal where the highest frequency component is f, and you sample at 2f then you can reproduce the original signal EXACTLY.
However, in order to re-construct for example a square wave you would need an infinite number of frequency components and there IS -theoretically- no highest frequency. But, this is only an issue for an "ideal" square wave, any real-world signal (including the sound from a musical instrument) will have a finite bandwidth. Moreover, your hearing can only pick up signal with a maximum frequency of about 20 kHz, so there is no need to record frequency components much higher than that (which is why 44 kHz is the CD standard, 2x20 kHz plus a few kHz to allow for the filtering)