《形式逻辑》中的直言三段论(正确式)之所以能成立,是因为有“中项是同一概念”的桥梁作用。然“中项是同一概念”中的“同一概念”常是人们争论焦点:有“同一种类概念”之说,有“同一词语”之说等。作者认为这“同一概念”应是就“概念间关系”而言的“全同关系”的“同一”或“从属关系”的“同一”。此外,别无其他形式的“同一”。 The reason why the orthodox syllogism (formal) in Formal Logic can be established is because of the bridge function of “the same term is the same concept.” However, “the same concept in the same concept” is often the focus of debate: there are “the same kind of concept”, “the same word” and so on. The author believes that this “same concept” should be “sameness” or “subordination” of “identical relations” in terms of “the relations among concepts”. In addition, there is no other form of “sameness.”