Revisiting Catastrophes. Thought of the Day 134.0

The most explicit influence from mathematics in semiotics is probably René Thom’s controversial theory of catastrophes (here and here), with philosophical and semiotic support from Jean Petitot. Catastrophe theory is but one of several formalisms in the broad field of qualitative dynamics (comprising also chaos theory, complexity theory, self-organized criticality, etc.). In all these cases, the theories in question are in a certain sense phenomenological because the focus is different types of qualitative behavior of dynamic systems grasped on a purely formal level bracketing their causal determination on the deeper level. A widespread tool in these disciplines is phase space – a space defined by the variables governing the development of the system so that this development may be mapped as a trajectory through phase space, each point on the trajectory mapping one global state of the system. This space may be inhabited by different types of attractors (attracting trajectories), repellors (repelling them), attractor basins around attractors, and borders between such basins characterized by different types of topological saddles which may have a complicated topology.

Catastrophe theory has its basis in differential topology, that is, the branch of topology keeping various differential properties in a function invariant under transformation. It is, more specifically, the so-called Whitney topology whose invariants are points where the nth derivative of a function takes the value 0, graphically corresponding to minima, maxima, turning tangents, and, in higher dimensions, different complicated saddles. Catastrophe theory takes its point of departure in singularity theory whose object is the shift between types of such functions. It thus erects a distinction between an inner space – where the function varies – and an outer space of control variables charting the variation of that function including where it changes type – where, e.g. it goes from having one minimum to having two minima, via a singular case with turning tangent. The continuous variation of control parameters thus corresponds to a continuous variation within one subtype of the function, until it reaches a singular point where it discontinuously, ‘catastrophically’, changes subtype. The philosophy-of-science interpretation of this formalism now conceives the stable subtype of function as representing the stable state of a system, and the passage of the critical point as the sudden shift to a new stable state. The configuration of control parameters thus provides a sort of map of the shift between continuous development and discontinuous ‘jump’. Thom’s semiotic interpretation of this formalism entails that typical catastrophic trajectories of this kind may be interpreted as stable process types phenomenologically salient for perception and giving rise to basic verbal categories.


One of the simpler catastrophes is the so-called cusp (a). It constitutes a meta-diagram, namely a diagram of the possible type-shifts of a simpler diagram (b), that of the equation ax4 + bx2 + cx = 0. The upper part of (a) shows the so-called fold, charting the manifold of solutions to the equation in the three dimensions a, b and c. By the projection of the fold on the a, b-plane, the pointed figure of the cusp (lower a) is obtained. The cusp now charts the type-shift of the function: Inside the cusp, the function has two minima, outside it only one minimum. Different paths through the cusp thus corresponds to different variations of the equation by the variation of the external variables a and b. One such typical path is the path indicated by the left-right arrow on all four diagrams which crosses the cusp from inside out, giving rise to a diagram of the further level (c) – depending on the interpretation of the minima as simultaneous states. Here, thus, we find diagram transformations on three different, nested levels.

The concept of transformation plays several roles in this formalism. The most spectacular one refers, of course, to the change in external control variables, determining a trajectory through phase space where the function controlled changes type. This transformation thus searches the possibility for a change of the subtypes of the function in question, that is, it plays the role of eidetic variation mapping how the function is ‘unfolded’ (the basic theorem of catastrophe theory refers to such unfolding of simple functions). Another transformation finds stable classes of such local trajectory pieces including such shifts – making possible the recognition of such types of shifts in different empirical phenomena. On the most empirical level, finally, one running of such a trajectory piece provides, in itself, a transformation of one state into another, whereby the two states are rationally interconnected. Generally, it is possible to make a given transformation the object of a higher order transformation which by abstraction may investigate aspects of the lower one’s type and conditions. Thus, the central unfolding of a function germ in Catastrophe Theory constitutes a transformation having the character of an eidetic variation making clear which possibilities lie in the function germ in question. As an abstract formalism, the higher of these transformations may determine the lower one as invariant in a series of empirical cases.

Complexity theory is a broader and more inclusive term covering the general study of the macro-behavior of composite systems, also using phase space representation. The theoretical biologist Stuart Kauffman (intro) argues that in a phase space of all possible genotypes, biological evolution must unfold in a rather small and specifically qualified sub-space characterized by many, closely located and stable states (corresponding to the possibility of a species to ‘jump’ to another and better genotype in the face of environmental change) – as opposed to phase space areas with few, very stable states (which will only be optimal in certain, very stable environments and thus fragile when exposed to change), and also opposed, on the other hand, to sub-spaces with a high plurality of only metastable states (here, the species will tend to merge into neighboring species and hence never stabilize). On the base of this argument, only a small subset of the set of virtual genotypes possesses ‘evolvability’ as this special combination between plasticity and stability. The overall argument thus goes that order in biology is not a pure product of evolution; the possibility of order must be present in certain types of organized matter before selection begins – conversely, selection requires already organized material on which to work. The identification of a species with a co-localized group of stable states in genome space thus provides a (local) invariance for the transformation taking a trajectory through space, and larger groups of neighboring stabilities – lineages – again provide invariants defined by various more or less general transformations. Species, in this view, are in a certain limited sense ‘natural kinds’ and thus naturally signifying entities. Kauffman’s speculations over genotypical phase space have a crucial bearing on a transformation concept central to biology, namely mutation. On this basis far from all virtual mutations are really possible – even apart from their degree of environmental relevance. A mutation into a stable but remotely placed species in phase space will be impossible (evolution cannot cross the distance in phase space), just like a mutation in an area with many, unstable proto-species will not allow for any stabilization of species at all and will thus fall prey to arbitrary small environment variations. Kauffman takes a spontaneous and non-formalized transformation concept (mutation) and attempts a formalization by investigating its condition of possibility as movement between stable genomes in genotype phase space. A series of constraints turn out to determine type formation on a higher level (the three different types of local geography in phase space). If the trajectory of mutations must obey the possibility of walking between stable species, then the space of possibility of trajectories is highly limited. Self-organized criticality as developed by Per Bak (How Nature Works the science of self-organized criticality) belongs to the same type of theories. Criticality is here defined as that state of a complicated system where sudden developments in all sizes spontaneously occur.

Contact Geometry and Manifolds


Let M be a manifold of dimension 2n + 1. A contact structure on M is a distribution ξ ⊂ TM of dimension 2n, such that the defining 1-form α satisfies

α ∧ (dα)n ≠ 0 —– (1)

A 1-form α satisfying (1) is said to be a contact form on M. Let α be a contact form on M; then there exists a unique vector field Rα on M such that

α(Rα) = 1, ιRα dα = 0,

where ιRα dα denotes the contraction of dα along Rα. By definition Rα is called the Reeb vector field of the contact form α. A contact manifold is a pair (M, ξ) where M is a 2n + 1-dimensional manifold and ξ is a contact structure. Let (M, ξ) be a contact manifold and fix a defining (contact) form α. Then the 2-form κ = 1/2 dα defines a symplectic form on the contact structure ξ; therefore the pair (ξ, κ) is a symplectic vector bundle over M. A complex structure on ξ is the datum of J ∈ End(ξ) such that J2 = −Iξ.

Let α be a contact form on M, with ξ = ker α and let κ = 1/2 dα. A complex structure J on ξ is said to be κ-calibrated if gJ [x](·, ·) := κ[x](·, Jx ·) is a JxHermitian inner product on ξx for any x ∈ M.

The set of κ-calibrated complex structures on ξ will be denoted by Cα(M). If J is a complex structure on ξ = ker α, then we extend it to an endomorphism of TM by setting

J(Rα) = 0.

Note that such a J satisfies

J2 =−I + α ⊗ Rα

If J is κ-calibrated, then it induces a Riemannian metric g on M given by

g := gJ + α ⊗ α —– (2)

Furthermore the Nijenhuis tensor of J is defined by

NJ (X, Y) = [JX, JY] − J[X, JY] − J[Y, JX] + J2[X, Y] for any X, Y ∈ TM

A Sasakian structure on a 2n + 1-dimensional manifold M is a pair (α, J), where

• α is a contact form;

• J ∈ Cα(M) satisfies NJ = −dα ⊗ Rα

The triple (M, α, J) is said to be a Sasakian manifold. Let (M, ξ) be a contact manifold. A differential r-form γ on M is said to be basic if

ιRα γ = 0, LRα γ = 0,

where L denotes the Lie derivative and Rα is the Reeb vector field of an arbitrary contact form defining ξ. We will denote by ΛrB(M) the set of basic r-forms on (M, ξ). Note that

rB(M) ⊂ Λr+1B(M)

The cohomology HB(M) of this complex is called the basic cohomology of (M, ξ). If (M, α, J) is a Sasakian manifold, then

J(ΛrB(M)) = ΛrB(M), where, as usual, the action of J on r-forms is defined by

Jφ(X1,…, Xr) = φ(JX1,…, JXr)

Consequently ΛrB(M) ⊗ C splits as

ΛrB(M) ⊗ C = ⊕p+q=r Λp,qJ(ξ)

and, according with this gradation, it is possible to define the cohomology groups Hp,qB(M). The r-forms belonging to Λp,qJ(ξ) are said to be of type (p, q) with respect to J. Note that κ = 1/2 dα ∈ Λ1,1J(ξ) and it determines a non-vanishing cohomology class in H1,1B(M). The Sasakian structure (α, J) also induces a natural connection ∇ξ on ξ given by

ξX Y = (∇X Y)ξ if X ∈ ξ

= [Rα, Y] if X = Rα

where the subscript ξ denotes the projection onto ξ. One easily gets

ξX J = 0, ∇ξXgJ = 0, ∇ξX dα = 0, ∇ξX Y − ∇ξY X = [X,Y]ξ,

for any X, Y ∈ TM. Consequently we have Hol(∇ξ) ⊆ U(n).

The basic cohomology class

cB1(M) = 1/2π [ρT] ∈ H1,1B(M)

is called the first basic Chern class of (M, α, J) and, if it vanishes, then (M, α, J) is said to be null-Sasakian.

Furthermore a Sasakian manifold is called α-Einstein if there exist λ, ν ∈ C(M, R) such that

Ric = λg + να ⊗ α, where Ric is the Ricci Tensor.

A submanifold p: L ֒→ M of a 2n + 1-dimensional contact manifold (M, ξ) is said to be Legendrian if :

1) dimRL = n,

2) p(TL) ⊂ ξ

Observe that, if α is a defining form of the contact structure ξ, then condition 2) is equivalent to say that p(α) = 0. Hence Legendrian submanifolds are the analogue of Lagrangian submanifolds in contact geometry.

Transcendentally Realist Modality. Thought of the Day 78.1


Let us start at the beginning first! Though the fact is not mentioned in Genesis, the first thing God said on the first day of creation was ‘Let there be necessity’. And there was necessity. And God saw necessity, that it was good. And God divided necessity from contingency. And only then did He say ‘Let there be light’. Several days later, Adam and Eve were introducing names for the animals into their language, and during a break between the fish and the birds, introduced also into their language modal auxiliary verbs, or devices that would be translated into English using modal auxiliary verbs, and rules for their use, rules according to which it can be said of some things that they ‘could’ have been otherwise, and of other things that they ‘could not’. In so doing they were merely putting labels on a distinction that was no more their creation than were the fishes of the sea or the beasts of the field or the birds of the air.

And here is the rival view. The failure of Genesis to mention any command ‘Let there be necessity’ is to be explained simply by the fact that no such command was issued. We have no reason to suppose that the language in which God speaks to the angels contains modal auxiliary verbs or any equivalent device. Sometime after the Tower of Babel some tribes found that their purposes would be better served by introducing into their language certain modal auxiliary verbs, and fixing certain rules for their use. When we say that this is necessary while that is contingent, we are applying such rules, rules that are products of human, not divine intelligence.

This theological language would have been the natural way for seventeenth or eighteenth century philosophers, who nearly all were or professed to be theists or deists, to discuss the matter. For many today, such language cannot be literally accepted, and if it is only taken metaphorically, then at least better than those who speak figuratively and frame the question as that of whether the ‘origin’ of necessity lies outside us or within us. So let us drop the theological language, and try again.

Well, here the first view: Ultimately reality as it is in itself, independently of our attempts to conceptualize and comprehend it, contains both facts about what is, and superfacts about what not only is but had to have been. Our modal usages, for instance, the distinction between the simple indicative ‘is’ and the construction ‘had to have been’, simply reflect this fundamental distinction in the world, a distinction that is and from the beginning always was there, independently of us and our concerns.

And here is the second view: We have reasons, connected with our various purposes in life, to use certain words, including ‘would’ and ‘might’, in certain ways, and thereby to make certain distinctions. The distinction between those things in the world that would have been no matter what and those that might have failed to be if only is a projection of the distinctions made in our language. Our saying there were necessities there before us is a retroactive application to the pre-human world of a way of speaking invented and created by human beings in order to solve human problems.

Well, that’s the second try. With it even if one has gotten rid of theology, unfortunately one has not gotten rid of all metaphors. The key remaining metaphor is the optical one: reflection vs projection. Perhaps the attempt should be to get rid of all metaphors, and admit that the two views are not so much philosophical theses or doctrines as ‘metaphilosophical’ attitudes or orientations: a stance that finds the ‘reflection’ metaphor congenial, and the stance that finds the ‘projection’ metaphor congenial. So, lets try a third time to describe the distinction between the two outlooks in literal terms, avoiding optics as well as theology.

To begin with, both sides grant that there is a correspondence or parallelism between two items. On the one hand, there are facts about the contrast between what is necessary and what is contingent. On the other hand, there are facts about our usage of modal auxiliary verbs such as ‘would’ and ‘might’, and these include, for instance, the fact that we have no use for questions of the form ‘Would 29 still have been a prime number if such-and- such?’ but may have use for questions of the form ‘Would 29 still have been the number of years it takes for Saturn to orbit the sun if such-and-such?’ The difference between the two sides concerns the order of explanation of the relation between the two parallel ranges of facts.

And what is meant by that? Well, both sides grant that ‘29 is necessarily prime’, for instance, is a proper thing to say, but they differ in the explanation why it is a proper thing to say. Asked why, the first side will say that ultimately it is simply because 29 is necessarily prime. That makes the proposition that 29 is necessarily prime true, and since the sentence ‘29 is necessarily prime’ expresses that proposition, it is true also, and a proper thing to say. The second side will say instead that ‘29 is necessarily prime’ is a proper thing to say because there is a rule of our language according to which it is a proper thing to say. This formulation of the difference between the two sides gets rid of metaphor, though it does put an awful lot of weight on the perhaps fragile ‘why’ and ‘because’.

Note that the adherents of the second view need not deny that 29 is necessarily prime. On the contrary, having said that the sentence ‘29 is necessarily prime’ is, per rules of our language, a proper thing to say, they will go on to say it. Nor need the adherents of the first view deny that recognition of the propriety of saying ‘29 is necessarily prime’ is enshrined in a rule of our language. The adherents of the first view need not even deny that proximately, as individuals, we learn that ‘29 is necessarily prime’ is a proper thing to say by picking up the pertinent rule in the course of learning our language. But the adherents of the first view will maintain that the rule itself is only proper because collectively, as the creators of the language, we or our remote answers have, in setting up the rule, managed to achieve correspondence with a pre-existing fact, or rather, a pre-existing superfact, the superfact that 29 is necessarily prime. The difference between the two views is, in the order of explanation.

The adherents regarding labels for the two sides, or ‘metaphilosophical’ stances, rather than inventing new ones, will simply take two of the most overworked terms in the philosophical lexicon and give them one more job to do, calling the reflection view ‘realism’ about modality, and the projection view ‘pragmatism’. That at least will be easy to remember, since ‘realism’ and ‘reflection’ begin with the same first two letters, as do ‘pragmatism’ and ‘projection’. The realist/pragmatist distinction has bearing across a range of issues and problems, and above all it has bearing on the meta-issue of which issues are significant. For the two sides will, or ought to, recognize quite different questions as the central unsolved problems in the theory of modality.

For those on the realist side, the old problem of the ultimate source of our knowledge of modality remains, even if it is granted that the proximate source lies in knowledge of linguistic conventions. For knowledge of linguistic conventions constitutes knowledge of a reality independent of us only insofar as our linguistic conventions reflect, at least to some degree, such an ultimate reality. So for the realist the problem remains of explaining how such degree of correspondence as there is between distinctions in language and distinctions in the world comes about. If the distinction in the world is something primary and independent, and not a mere projection of the distinction in language, then how the distinction in language comes to be even imperfectly aligned with the distinction in the world remains to be explained. For it cannot be said that we have faculties responsive to modal facts independent of us – not in any sense of ‘responsive’ implying that if the facts had been different, then our language would have been different, since modal facts couldn’t have been different. What then is the explanation? This is the problem of the epistemology of modality as it confronts the realist, and addressing it is or ought to be at the top of the realist agenda.

As for the pragmatist side, a chief argument of thinkers from Kant to Ayer and Strawson and beyond for their anti-realist stance has been precisely that if the distinction we perceive in reality is taken to be merely a projection of a distinction created by ourselves, then the epistemological problem dissolves. That seems more like a reason for hoping the Kantian or Ayerite or Strawsonian view is the right one, than for believing that it is; but in any case, even supposing the pragmatist view is the right one, and the problems of the epistemology of modality are dissolved, still the pragmatist side has an important unanswered question of its own to address. The pragmatist account, begins by saying that we have certain reasons, connected with our various purposes in life, to use certain words, including ‘would’ and ‘might’, in certain ways, and thereby to make certain distinctions. What the pragmatist owes us is an account of what these purposes are, and how the rules of our language help us to achieve them. Addressing that issue is or ought to be at the top of the pragmatists’ to-do list.

While the positivist Ayer dismisses all metaphysics, the ordinary-language philosopher Strawson distinguishes good metaphysics, which he calls ‘descriptive’, from bad metaphysics, which he calls ‘revisionary’, but which rather be called ‘transcendental’ (without intending any specifically Kantian connotations). Descriptive metaphysics aims to provide an explicit account of our ‘conceptual scheme’, of the most general categories of commonsense thought, as embodied in ordinary language. Transcendental metaphysics aims to get beyond or behind all merely human conceptual schemes and representations to ultimate reality as it is in itself, an aim that Ayer and Strawson agree is infeasible and probably unintelligible. The descriptive/transcendental divide in metaphysics is a paradigmatically ‘metaphilosophical’ issue, one about what philosophy is about. Realists about modality are paradigmatic transcendental metaphysicians. Pragmatists must in the first instance be descriptive metaphysicians, since we must to begin with understand much better than we currently do how our modal distinctions work and what work they do for us, before proposing any revisions or reforms. And so the difference between realists and pragmatists goes beyond the question of what issue should come first on the philosopher’s agenda, being as it is an issue about what philosophical agendas are about.

Derivability from Relational Logic of Charles Sanders Peirce to Essential Laws of Quantum Mechanics


Charles Sanders Peirce made important contributions in logic, where he invented and elaborated novel system of logical syntax and fundamental logical concepts. The starting point is the binary relation SiRSj between the two ‘individual terms’ (subjects) Sj and Si. In a short hand notation we represent this relation by Rij. Relations may be composed: whenever we have relations of the form Rij, Rjl, a third transitive relation Ril emerges following the rule

RijRkl = δjkRil —– (1)

In ordinary logic the individual subject is the starting point and it is defined as a member of a set. Peirce considered the individual as the aggregate of all its relations

Si = ∑j Rij —– (2)

The individual Si thus defined is an eigenstate of the Rii relation

RiiSi = Si —– (3)

The relations Rii are idempotent

R2ii = Rii —– (4)

and they span the identity

i Rii = 1 —– (5)

The Peircean logical structure bears resemblance to category theory. In categories the concept of transformation (transition, map, morphism or arrow) enjoys an autonomous, primary and irreducible role. A category consists of objects A, B, C,… and arrows (morphisms) f, g, h,… . Each arrow f is assigned an object A as domain and an object B as codomain, indicated by writing f : A → B. If g is an arrow g : B → C with domain B, the codomain of f, then f and g can be “composed” to give an arrow gof : A → C. The composition obeys the associative law ho(gof) = (hog)of. For each object A there is an arrow 1A : A → A called the identity arrow of A. The analogy with the relational logic of Peirce is evident, Rij stands as an arrow, the composition rule is manifested in equation (1) and the identity arrow for A ≡ Si is Rii.

Rij may receive multiple interpretations: as a transition from the j state to the i state, as a measurement process that rejects all impinging systems except those in the state j and permits only systems in the state i to emerge from the apparatus, as a transformation replacing the j state by the i state. We proceed to a representation of Rij

Rij = |ri⟩⟨rj| —– (6)

where state ⟨ri | is the dual of the state |ri⟩ and they obey the orthonormal condition

⟨ri |rj⟩ = δij —– (7)

It is immediately seen that our representation satisfies the composition rule equation (1). The completeness, equation (5), takes the form

n|ri⟩⟨ri|=1 —– (8)

All relations remain satisfied if we replace the state |ri⟩ by |ξi⟩ where

i⟩ = 1/√N ∑n |ri⟩⟨rn| —– (9)

with N the number of states. Thus we verify Peirce’s suggestion, equation (2), and the state |ri⟩ is derived as the sum of all its interactions with the other states. Rij acts as a projection, transferring from one r state to another r state

Rij |rk⟩ = δjk |ri⟩ —– (10)

We may think also of another property characterizing our states and define a corresponding operator

Qij = |qi⟩⟨qj | —– (11)


Qij |qk⟩ = δjk |qi⟩ —– (12)


n |qi⟩⟨qi| = 1 —– (13)

Successive measurements of the q-ness and r-ness of the states is provided by the operator

RijQkl = |ri⟩⟨rj |qk⟩⟨ql | = ⟨rj |qk⟩ Sil —– (14)


Sil = |ri⟩⟨ql | —– (15)

Considering the matrix elements of an operator A as Anm = ⟨rn |A |rm⟩ we find for the trace

Tr(Sil) = ∑n ⟨rn |Sil |rn⟩ = ⟨ql |ri⟩ —– (16)

From the above relation we deduce

Tr(Rij) = δij —– (17)

Any operator can be expressed as a linear superposition of the Rij

A = ∑i,j AijRij —– (18)


Aij =Tr(ARji) —– (19)

The individual states could be redefined

|ri⟩ → ei |ri⟩ —– (20)

|qi⟩ → ei |qi⟩ —– (21)

without affecting the corresponding composition laws. However the overlap number ⟨ri |qj⟩ changes and therefore we need an invariant formulation for the transition |ri⟩ → |qj⟩. This is provided by the trace of the closed operation RiiQjjRii

Tr(RiiQjjRii) ≡ p(qj, ri) = |⟨ri |qj⟩|2 —– (22)

The completeness relation, equation (13), guarantees that p(qj, ri) may assume the role of a probability since

j p(qj, ri) = 1 —– (23)

We discover that starting from the relational logic of Peirce we obtain all the essential laws of Quantum Mechanics. Our derivation underlines the outmost relational nature of Quantum Mechanics and goes in parallel with the analysis of the quantum algebra of microscopic measurement.

Category-Theoretic Sinks

The concept dual to that of source is called sink. Whereas the concepts of sources and sinks are dual to each other, frequently sources occur more naturally than sinks.

A sink is a pair ((fi)i∈I, A), sometimes denoted by (fi,A)I or (Aifi A)I consisting of an object A (the codomain of the sink) and a family of morphisms fi : Ai → A indexed by some class I. The family (Ai)i∈I is called the domain of the sink. Composition of sinks is defined in the (obvious) way dual to that of composition of sources.


In Set, a sink (Aifi A)I is an epi-sink if and only if it is jointly surjective, i.e., iff A = ∪i∈I fi[Ai]. In every construct, all jointly surjective sinks are epi-sinks. The converse implication holds, e.g., in Vec, Pos, Top, and Σ-Seq. A category A is thin if and only if every sink in A is an epi-sink.