Free association

In the early 1880s, the Viennese physician Josef Breuer treated a young woman known in the case notes as Anna O. She found that talking through whatever was on her mind, at length, eased her symptoms. She called it "the talking cure".

Breuer's younger colleague Sigmund Freud took the idea further. At first he used hypnosis, then pressed his hand on patients' foreheads and insisted a memory would come. Over the 1890s he gave both up for something simpler: the patient lay down, and said whatever came to mind.

Freud called it the fundamental rule. Say everything, he told patients, even when a thought seems unimportant, irrelevant, embarrassing or rude. He compared it to sitting by the window on a train and describing the passing view to someone who can't see it: you report what goes by, you don't choose it.

The rule matters because of what we normally do. In ordinary talk, and in ordinary thinking, we edit constantly: we stay on topic, skip what's awkward and drop what seems pointless. Freud thought the edits were where the interesting material was. The thought you were about to leave out is often the one that matters.

Halfway through writing about her week, Amira thinks of her old piano teacher, which seems to have nothing to do with anything. Following Freud's rule, what should she do?

Freud believed free association led, step by step, to buried memories and wishes. There's little good evidence for that, and it's easy for a listener to read whatever they expect into what comes out.

A close cousin has been tested, though. In the 1980s, the psychologist James Pennebaker asked students to write for about 15 minutes a day, over a few days, about their deepest thoughts and feelings on something that troubled them. Over the following months they visited the health center less than students who wrote about everyday topics. Many studies since have found small benefits from this kind of expressive writing, not large ones.

One warning. If the writing just goes round the same worries, it's turned into rumination. Stop, and do something else.