这本书的主题——深度学习是通向人工智能的途径之一。具体来说，它
是机器学习的一种，一种能够使计算机系统从经验和数据中得到提高的技术。我们
坚信机器学习可以构建出在复杂实际环境下运行的AI 系统，并且是唯一切实可行的
方法。深度学习是一种特定类型的机器学习，具有强大的能力和灵活性，它将大千
世界表示为嵌套的层次概念体系（由较简单概念间的联系定义复杂概念、从一般抽
象概括到高级抽象表示）(The subject of this book, deep learning, is one of the ways to artificial intelligence. In particular, it is a kind of machine learning, a technology that can improve the computer system from experience and data. We firmly believe that machine learning can build a AI system that runs in a complex and practical environment, and is the only practical way to do it. Deep learning is a specific type of machine learning, with strong ability and flexibility. It represents the world as a nested hierarchical concept system, which is defined by complex concepts, from general abstract to high-level abstract.)