In a recent article, Barrett & Halvorson (2016) define a notion of equivalence for first-order theories, which they call “Morita equivalence.” To argue that Morita equivalence is a reasonable measure of “theoretical equivalence,” they make use of the claim that Morita extensions “say no more” than the theories they are extending. The goal of this article is to challenge this central claim by raising objections to their argument for it and by showing why there is good reason to think that the claim itself is false. In light of these criticisms, this article develops a natural way for the advocate of Morita equivalence to respond. I prove that this response makes her criterion a special case of bi-interpretability, an already well-established barometer of theoretical equivalence. I conclude by providing reasons why the advocate of Morita equivalence should opt for a notion of theoretical equivalence that is defined in terms of interpretability rather than Morita extensions.

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关于森田的等效性和可解释性

在最近的一篇文章中，Barrett & Halvorson (2016) 为一阶理论定义了一个等价概念，他们称之为“Morita 等价”。为了争辩说森田等价是“理论等价”的合理衡量标准，他们利用了森田扩展比他们正在扩展的理论“不说更多”的主张。本文的目的是通过对他们的论点提出反对意见来挑战这一核心主张，并说明为什么有充分的理由认为该主张本身是错误的。鉴于这些批评，本文为森田对等的倡导者提出了一种自然的回应方式。我证明这种反应使她的标准成为双向可解释性的特例，一个已经确立的理论等效性晴雨表。