 Observations about such formally similar but semantically dissimilar phrases led the Mohists to doubt that complex linguistic structures have any regular or reliable relation to the patterns of similarity and difference that ground their correct use. Formal parallels between the words and phrases we use to talk about things can guide us in discriminating kinds only up to a point, because linguistic similarities may not reflect actual similarities in things. In classical Chinese, ‘oxen-and-horses’ (niú mǎ 牛馬) and ‘white horse’ (bái mǎ 白馬) have a similar formal structure, but the first denotes the sum of two kinds of things, the second a portion of one kind of thing. Formal similarities in linguistic structure are thus an unreliable guide to distinguishing kinds. To discriminate kinds properly, we need to examine the semantic criteria (yīn 因) or grounds (gù 故) that determine the proper use of the words or phrases that denote them, and not rely only on structural similarities to other words or phrases. In some cases, we may need to point out that structurally similar expressions in fact have very different semantics. This is a key theme of the “Lesser Selection” (Xiǎo Qǔ), a brief summary and illustration of Mohist dialectics that is probably the most important text in the history of Chinese logic. 