阴阳学说是中国古代的一种宇宙观和方法论，具有对立统一的内涵。阴阳是对自然界相互关联的某些事物或现象对立双方的概括。阴阳既可以代表两种相互对立的事物或势力，也可以代表同一事物内部所存在的相互对立的两个方面。

　　The theory of yin-yang is a perspective and methodology originated in ancient China with the unity¹ of opposites being its central premise². Yin-Yang is the generalization³ of the two opposite aspects of things or phenomena⁴ which are interrelated in the natural worlds. Yin and yang represent not only the two inter-opposite things or forces, but also the two inter-opposite aspects existing within one object.

　　用阴阳来概括某些事物或现象的对立统一关系必须具备两个条件：对立事物或现象具有相关性和阴阳属性的规定性。

　　Two requirements must be met when we describe the unity of opposites in terms of yin-yang: relativity, the interrelationship between the opposites, and property stipulation⁵, the rules defining the properties of Yin-Yang.

　　相关性是指这些事物或现象必须是属于同一统一体中的相互关联的事物或现象，而不是毫不相干的。如水与火乃是自然界中物质存在的不同状态和现象，两者是相互关联而又相互对立的。水性寒而下走，火性热而上炎，故水属阴，火属阳。实际上，阴阳学说中的阴阳，仅是抽象的属性概念，而非指互不相关的具体事物。

　　Relativity refers to the fact that things or phenomena must belong to the same unity and be interrelated with each other. For example, water and fire are different states and phenomena of material existence in the nature. They are interrelated and inter-opposed. Water is cold in nature and flows downward while fire is hot and flames upward. So water pertains⁶ to yin and fire to yang. In fact, yin and yang in the theory are just an abstract conception of properties. They are not the actually uninterrelated objects themselves.

　　阴阳属性的规定性是指阴或阳不仅能概括事物或现象对立统一的两个方面，而且还代表着这两个方面的一定属性。也就是说，自然界相互关联的事物或现象对立的两个方面，本身就具有截然相反的两种属性。阳代表积极、进取、刚强等特性和具有这些特性的事物或现象；阴代表消极、退守、柔弱等特性和具有这些特性的事物和现象。而事物或现象相互对立的两个方面的阴阳属性是相对而言的，是由事物或现象的性质、位置、趋势等因素所决定的。

　　The property stipulation means that yin or yang are used to both describe the two opposite aspects in the same unity and represent the certain properties of the two opposing aspects. It means the two naturally interrelated opposite aspects of an object or phenomenon have different properties of their own: yang equal to that of activeness, progressiveness, and firmness and things or phenomena of these properties , and yin that of inactiveness, decline, and softness and things or phenomena of these properties. But the properties of yin and yang possessed⁷ by two opposing two aspects should not be defined arbitrarily or inverted⁸ randomly⁹ because of the properties' relativity. They are determined¹⁰ by such factors as their nature, position, or tendencies.

　　阴阳学说认为，自然界中的一切事物都存在着相互对立的阴阳两个方面，这两个方面的运动变化乃是一切事物构成和发展变化的根本原因。阴阳的对立统一乃是物质世界运动变化的总纲。中医学认为阴阳是自然界的根本规律，是事物生长、发展、变化、衰亡的根源。

　　According to the theory of yin-yang, everything in the natural world is made up of two opposing aspects - yin and yang, and the constant changes of their relations are the root cause of the formation and development of the world. Unity of opposites is the general principles of the development of the material world. TCM holds that yin-yang is both the fundamental law in the natural world and the origin of growth, development, change, and decline.

　　下表是对阴阳理论事物属性的一个简单概括。

　　The table below is a brief summary of the theory of yin-yang

　　事物/现象 things/phenomena

　　阴阳属性分类 Category of Properties of Yin and Yang

　　阴Yin

　　阳Yang

　　空间Space

　　上、外Up and outside

　　下、内Down and inside

　　时间Time

　　昼Day

　　夜Night

　　季节Season

　　春、夏Spring and summer

　　秋、冬Autumn and winter

　　温度Temperature

　　温、热Warm and hot

　　凉、寒Cool and cold

　　湿度Humidity

　　干燥Dry

　　湿润Moist

　　重量Weight

　　轻Light

　　重Heavy

　　亮度Brightness

　　明亮Bright

　　晦暗Dim

　　运动状态　　State of movement

　　上升、动、兴奋、亢进　　Ascending motion, excited or hyperactive

　　下降、静、抑制、衰退　　Descending motion, quiescence , inhibition, decline