皮亚杰认为符号表征是认知发展的核心，将表征本质随年龄所发生的变化看作是区分发展阶段的主要特征。从根本上看，符号表征是指个体用来代表其他事物的东西。
一旦语言从2岁左右开始发展，他们就有了一个符号表征系统，可以谈论过去和现在环境之外的事情。
Once language starts to develop from about age 2, they do have a system for symbolic representation and can talk about things which aren't in their immediate environment including the past.
在上世纪六十年代以前，语言的符号表征一直被视为是人类的专利。
Until the 1960s, symbolic representation of language was thought to be uniquely human.
我先采用一个简单的定义：计算机是一个根据规则处理符号表征的仪器。
I shall instead assume the following rough definition of what a computer is: it is a device which processes representations according to rules.
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