Let’s take a look now at the rule of transitivity. Consider this triangle of connected elements:

The rule of transitivity for a simple equivalence relation states that if a ∼ b and b ∼ c, then a ∼ c. We can recast this in terms of truth values as follows: it is never more true that a ∼ b and b ∼ c than it is true that a ∼ c. In other words:
Rule of transitivity: Id(a, b) ∩ Id(b, c) ⊆ Id(a, c)
The question is, what is the meaning of “and” (∩) in this statement? The intuitive notion which I will take as my guide here is this: a chain is as strong as its weakest link. In other words, the truth-value Id(a, b) ∩ Id(b, c) is never stronger than the weakest of the two truth-values Id(a, b) and Id(b, c). It follows, therefore, that the truth-value Id(a, c) is always at least as strong as the weakest of these two truth values.
However, as the “diamond” example with which I closed my last post shows, it is not always as simple as saying that one truth-value is stronger than another: in that example, while it’s clear that 0 ⊆ 1, there is no way to decide which of ⌊ and ⌋ is the stronger. We will shortly have need of another pair of concepts, which Badiou calls the “conjunction” and “envelope” of truth-values.
First of all, however, let’s consider the above rewritten rule of transitivity in the case where Ω = {0, 1}. Here, it’s quite simple:
i) If both Id(a, b) and Id(b, c) are 1, then it is completely true that a ∼ b ∧ b ∼ c, so the value of Id(a, b) ∩ Id(b, c) is also 1. It then follows, since this value cannot be greater than that of Id(a, c) that Id(a, c) is also 1: it is completely true that a ∼ c.
ii) If either (or both) of Id(a, b) and Id(b, c) is 0, then it is completely false that a ∼ b ∧ b ∼ c, so the value of Id(a, b) ∩ Id(b, c) must be 0. It does not follow that Id(a, c) must also be 0, since Id(a, c) may be greater than the conjoined values of Id(a, b) and Id(b, c).
iii) If Id(a, c) = 0 then either or both of Id(a, b) and Id(b, c) must be 0.
We can see, then, that in the simplest case, where there is never any ambiguity about which of two truth-values is the stronger, the rewritten rule of transitivity supports the transitive property of a plain equivalence relation. But we now need to give a sense to the symbol ∩ (“conjunction”) that will still be meaningful when neither Id(a, b) ⊆ Id(b, c) nor Id(b, c) ⊆ Id(a, b).
The concept we need here is that of the greatest lower bound (g.l.b) of any two (or more) values. Simply put, the g.l.b. of a set P of truth-values is the strongest truth-value x such that for all y ε P, x ⊆ y. This is the value that Badiou calls the “conjunction” of two or more truth-values.
In our previous “diamond” example, the g.l.b. of ⌊ and ⌋ is simply 0: there is no truth-value greater than 0 that is less than or equal to both ⌊ and ⌋. The “left-deviation” and “right-deviation” are thus absolutely disjunct: they have no truth in common (although the maximum truth value, 1, is the least upper bound, or “envelope” in Badiou’s terminology, of both). Moreover, the g.l.b. of 1 and ⌊ is ⌊, and the g.l.b. of 1 and ⌋ is ⌋ – generally, 1 ∩ x = x, while 0 ∩ x = 0.
We can now answer the question posed at the end of the previous post: given
Id(a, c) = ⌊
Id(b, c) = ⌋
what can be the value of Id(a, b)? It must be such that Id(a, b) ∩ ⌋ ⊆ ⌊; thus, it can be either ⌊ (in which case Id(a, b) ∩ Id(b, c) = ⌊ ∩ ⌋ = 0), or 0 (with the same result). It cannot be ⌋, because ⌋ ∩ ⌋ = ⌋, and it is not the case that ⌋ ⊆ ⌊. For the same reason, it cannot be 1.
We can see, then, that the truth-value of a ∼ c constrains the truth-values of a ∼ b and b ∼ c, according to the logic of conjunction: the nature of this constraint will depend on the order-structure of Ω. What is starting to emerge here is a sense of the logical compatibility of the connections between elements of an object, the necessity that the diagram of its interior network of relations submit to the regulation of a “transcendental” which prescribes which patterns of interconnectedness are logically compatible and which are not. It is on this basis that the entire phenomenal complexity of the object can be unfolded and analysed.
My sense of it is that “compatibility” is the successor notion to “consistency” in Badiou’s ontological thinking: that while it belongs to beings merely to “consist” as multiples, the world of objects is one of compatible (or perhaps “compossible”) appearances. When we speak in a vaguely Latourian fashion of networks of entities engaged in shifting patterns of alliance and contestation, or in a Deleuzian manner of “rhizomes” in which connections proliferate without reference to any master signifier or phallic command-centre, we have not yet begun to address the question of how such structures generate their own internal constraints, or what the logical contexture of such constraints might be. This, I think, is where Badiou’s mapping of the transcendental of appearance marks a significant “move” with respect to the philosophy of things and the worlds in which they reside and combine.
In the next post, I’ll go on to look at the rule of reflexivity, and the way in which this rule can be rewritten so as to accommodate different degrees of existence – including, crucially, the zero-degree of inexistence.