告子上 · 第 02 / 20 章 · 孟子 6A.2
《孟子·告子上》6A.2：人性像水吗，为什么孟子仍说性善
告子说人性像水，决东则东、决西则西，似乎无分善不善；孟子回应，水虽不分东西，却分上下，人性也有其基本趋向。
告子曰：「性，犹湍水也。决诸东方则东流，决诸西方则西流。人性之无分于善不善也，犹水之无分于东西也。」孟子曰：「水信无分于东西，无分于上下乎？人性之善也，犹水之就下也。人无有不善，水无有不下。今夫水：搏而跃之，可使过颡；激而行之，可使在山。是岂水之性哉？其势则然也。人之可使为不善，其性亦犹是也。」
英文参考译文
The philosopher Gao said, 'Man's nature is like water whirling round in a corner. Open a passage for it to the east, and it will flow to the east; open a passage for it to the west, and it will flow to the west. Man's nature is indifferent to good and evil, just as the water is indifferent to the east and west.' Mencius replied, 'Water indeed will flow indifferently to the east or west, but will it flow indifferently up or down? The tendency of man's nature to good is like the tendency of water to flow downwards. There are none but have this tendency to good, just as all water flows downwards. Now by striking water and causing it to leap up, you may make it go over your forehead, and, by damming and leading it you may force it up a hill - but are such movements according to the nature of water? It is the force applied which causes them. When men are made to do what is not good, their nature is dealt with in this way.'
重点修订页
人工补强的解释层
核心问题
为什么孟子用“水无分于东西，无分于上下乎”反驳告子？
直接回答
因为他要区分“可被外力改向”与“本来趋向为何”。水当然能被决向东西，但它终究往下走；人也会受环境牵引，可这不等于其根本趋向对善恶完全中立。
第一性原理
判断一个东西的本性，不能只看它在外力作用下会怎么偏转，更要看它脱离扭曲后自然会朝哪里去。
为什么重要
这章适合承接“人性像水”“孟子反驳告子”“human nature and the water analogy”这类高意图搜索，是性善论核心页面。
延伸阅读
这章在做什么
这章是《告子上》第 2 / 20 章，最直接的进入线索是“性，犹湍水也”。放回全卷，它讨论的是性善、欲望与告子论辩，并可与性善、仁政互相印证。
更宽的搜索入口
如果你带着更宽的问题进入这一章，先从正确的 hub 页进入
全卷语境
《告子上》是性善论与告子论辩的核心战场。
引用提示
不要把它读成孟子否认环境影响。孟子承认水会被击打飞溅、人会被环境扭曲，他守的是：扭曲不等于本向。