This essay opposes two forms of instrumentalism: a stronger and its weaker version. The strong version states that abductive inference is invalid, thus it is legitimate to renounce theoretical belief. It is argued that the instrumentalists’ proposal is incoherent since there is no difference between believing a theory and using it. According to the weaker form, the justification for theoretical belief can be nothing more than pragmatic since abductive inference is invalid. It is argued that contrary to initial appearances, the burden of proving that abductive inference is invalid lies with the instrumentalist and not the realist.
Keywords: instrumentalism, abductive inference, scientific theory, theoretical belief,