What is a theory of change?

Policy interventions are sometimes pitched as magic solutions: 'If you lower taxes enough, the economy will automatically create jobs.' Or 'if you give students computers, they'll automatically get better grades at school.' This is the language favoured by politicians, who need to have catchy headlines next to their photos in newspapers. This is simple language.

File:Genie Lamps 007.JPG - Wikimedia Commons
Politicians are genies. Image source.

When it comes to formulating and implementing your intervention in the real world, these simple mental models don't work anymore. Things should no longer be thought of as automatic. There should be something in the middle that joins our lever to a fulcrum that makes it pull a rope that opens a lid that lets the food fall down into your cat's bowl. Thus, policy analists (contrary to politicians) tend to see interventions as Rube Goldberg machines:

A self-operating napkin, designed by Rube Goldberg.

Our Rube Goldberg machines are called theories of change (ToC.) They simplify how the world works so we can figure out how our intervention is supposed to create the intended impact. Like this one, for instance:

A ToC for a microcredit intervention, by IPA. Source.

As with Rube-Goldberg machines, there's a myriad things that can go wrong when you implement an intervention. But it's better to know what can go wrong and what you can do about it than simply expecting that a genie will somehow make things work.