Simple Theories

Before we look at Theories of Change in particular, we look at Theories in general. All Theories are built up of simple Theories, like this:

Student satisfaction with school

 Student feels they live up to expectations

 Student feels fulfilled

 Student feels supported and liked

A single child Variable is predicted by one or more parent Variables.

Here we can see a simple Theory predicting Student satisfaction with school.

In a later Chapter we will look at what the new red symbols mean.

A Variable, called the consequence Variable, followed on successive lines by one or more different Variables, called Influence Variables, each indented by one space, is called a simple Theory.

The consequence Variable

 An influence Variable

 Another influence Variable

The consequence Variable may include a phrase beginning “!Rule”, which describes how the Consequence is influenced by the influence Variables, see chapter xx.


A simple Theory claims that the consequence Variable is directly influenced by the influence Variables. Any Rule, if specified, says how it is influenced on the basis of the Levels of the influence Variables. Concretely, (Pearl 2000) it means if the influence Variables are forced, manipulated, to take such-and-such Levels, the consequence Variable will take whatever Level is specified for it by the Rule.

In the corresponding diagram, arrows go from the Influences to the Consequence.

Theorymaker shows how causal claims can be represented in terms of relationships between Variables governed by Rules. But behind this is a strong thesis, namely that all causal claims can be represented as relationships between Variables.

In the simple Theory below, C is the consequence Variable, A and B are the influence Variables.

C !Rule: some Rule



So in the written version, you can see that Theorymaker shows the Influences of a Variable by listing them below it, indented by one space.

Some people prefer their Theories bottom-up, or top-down, rather than this left-to-right orientation. We’ll talk about these stylistic preferences and their metaphysical baggage in chapter xx.

You could argue, explanations or causal narratives (between Variables), aka simple Theories, are actually the primary phenomenon and Variables themselves are secondary.

Theories and Mechanisms

This is all very well, but Theories contain Statements, and when we are doing evaluation we don’t always want to talk about sentences or Statements, we want to talk about things. We want to talk about the Mechanisms which Theories are true of.

Yes. For example, it is much more natural to say

The Mechanism by which unconditional cash transfers are supposed to benefit women is not really clear

rather than something like:

There is no clear and agreed Theory which leads from unconditional cash transfers to benefits for women

… after all, it is not quite the same to talk about what Theories people might have; sometimes we just want to talk about the Mechanisms without worrying about who believes or says what.

Theories are human products - stories we construct to say how some part of the world works (Wallis 2015).

So Theorymaker native speakers have another Word in Capitals: Mechanism.

A “Mechanism” is just whatever the corresponding Theory is about. Theorymaker native speakers say: A Theory reports a Mechanism. But you could also say “A Theory reflects a Mechanism” or “A Theory is about a Mechanism” or “A Theory is the assertion of a Mechanism”.

Theories can be more or less true or accurate..11 So we can say “hmm, look how the children’s school-work is influenced by the behaviour of their peers - what an interesting Mechanism, let’s try and make an adequate Theory of this Mechanism”.

Mechanisms in Realistic Evaluation

We are using the word Mechanism here in something like the broad sense in which it is used in realistic evaluation Theory (Pawson & Tilley, 1997). There is a special brief chapter on Realist Evaluation.


Pearl, Judea. 2000. Causality: Models, reasoning and inference. Cambridge Univ Press.

Wallis, Steven E. 2015. “The Science of Conceptual Systems: A Progress Report.” Foundations of Science. Springer Netherlands. doi:10.1007/s10699-015-9425-z.

  1. Philosophers will recognise this as so-called “correspondence theory of truth” with all the advantages and disadvantages xx