Many phenomena in the natural world are complex, so scientists study them through simplified and idealised models. Philosophers of science have sought to explain how these models relate to the world. On most accounts, models do not represent the world directly, but through target systems. However, our knowledge of target systems is incomplete. First, what is the process by which target systems come about? Second, what types of entity are they? I argue that the basic conception of target systems, on which other conceptions depend, is as parts of the world. I outline the process of target system specification and show that it is a crucial step in modelling. I also develop an account of target system evaluation, based on aptness. Paying close attention to target system specification and evaluation can help scientists minimise the frequency and extent of mistakes, when they are using models to investigate phenomena in complex real-world systems.

中文翻译：

---

什么是目标系统？

自然界中的许多现象都很复杂，因此科学家们通过简化和理想化的模型来研究它们。科学哲学家试图解释这些模型与世界的关系。在大多数情况下，模型不直接代表世界，而是通过目标系统。然而，我们对目标系统的了解并不完整。首先，目标系统的产生过程是怎样的？其次，它们是什么类型的实体？我认为，其他概念所依赖的目标系统的基本概念是作为世界的一部分。我概述了目标系统规范的过程，并表明它是建模的关键步骤。我还开发了一个基于 aptness 的目标系统评估帐户。