Noncausal Behavior of Classical Tachyons

It is shown by example that causality violation can take place through the transmission of classical tachyons between three or more observers in such a way that each observer receives and emits only tachyons whose energies he measures to be positive. Such examples are not open to the ambiguities of interpretation proposed by Feinberg; they imply that a classical-particle description of tachyons is not physically viable.