From the greek “synth” (“together”) and “ethesia” (“perception”).
For people who are not synaesthetes, information will typically activate one sense. For example, when you listen to music, you hear the music.
For people who are synaesthetes, however, this is different. Information can activate different senses than typical, or even multiple senses. For example, when listening to music, you may hear the music, and also taste it, or see what colour it is.
Being able to see music is a common form of synaesthesia, but any of the senses can overlap.
Synaesthesia is involuntary: you can’t make it happen, and you can’t make it not happen. There are many different types of synaesthesia. Some people will have more than one type. Some people who use psychedelic drugs can have a short experience of synaesethesia during a trip.
Words or numbers might have colours or personalities.
“2” might be kind.
“Wednesday” might be green.
You might be able to taste sentences, or smell sounds.
The chime of a bell might taste sour.
Synaesthesia appears to be genetic, and is typically present from childhood, although it can also develop in adulthood.
Autistic people are about 3 times more likely to experience this than non-autistic people.
Some synaesthetes find the experience isolating, but many enjoy being a synaesthete.
Melissa McCracken is a synaesthetic artist who paints songs.