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.

A Variable label, followed on successive lines by one or more (usually different) Variable labels, each indented by one space, is called a simple Theory.

Usually we will just refer to these Variable labels as “Variables”.

The indented Variables are called the parent or influence Variables and the first Variable is called the child or consequence Variable. We also say that a parent Variable is upstream of its children, which are downstream of its parent(s).

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.

In the corresponding diagram, arrows go from the Influence(s) to the Consequence.

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.

Note that we haven’t provided a translation between Variables and English. Variables only have a meaning when they appear inside Theories.

Note we say “if the influence Variables are manipulated to take such-and-such Levels” rather than “if the influence Variables are observed to take such-and-such Levels”. Theorymaker, following (Pearl 2000), is thoroughly causal, not correlational.

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 and even weakly causal claims can be represented as relationships between Variables. With “weakly causal”, we explicitly cover also relationships in which the Influencers make some kind of difference, even when they don’t completely determine the Consequence.

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




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.


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