Weak measurements measure probability amplitudes (and very little else)

• Weak measurement on a pre- and post-selected system is a particular perturbative scheme.
• A conventional average for the additional degree of freedom measured.
• The result is proportional to the amplitudes on the virtual paths connecting two system's states.
• Over-interpretation of the weak values (WV) is unwise.
• “Unusual” WVs are not unusual after all.

Conventional quantum mechanics describes a pre- and post-selected system in terms of virtual (Feynman) paths via which the final state can be reached. In the absence of probabilities, a weak measurement (WM) determines the probability amplitudes for the paths involved. The weak values (WV) can be identified with these amplitudes, or their linear combinations. This allows us to explain the “unusual” properties of the WV, and avoid the “paradoxes” often associated with the WM.