Grapheme-temperature synesthesia

With this type of synesthesia, numbers and letters (or in some cases phonemes, lexemes, syllables or whole words) are perceived as having a particular temperature. It can take the form of a “duality synesthesia”, where letters, numbers and other concepts fall into one of two categories – hot or cold – or they might be on a scale, going from warmer to cooler. The temperature is probably perceived as a mere association in the synesthete’s mind and they would only rarely feel a real temperature sensation with physical manifestations like shivering from the cold or sweating with the heat.

Sometimes, for grapheme-colour synesthetes, the temperature of a letter or number is part and parcel of its synesthetic colour, so a red letter would be hot, for example, while a blue letter would be perceived as cold. If the person in question has ordinal linguistic personification and associates their letters and numbers with different personalities, a higher temperature can correspond to a warmer, more loving personality and a cooler temperature to a grapheme that is also cold in its personal relationships. One of the synesthetes in the examples below say that their letters and words have a certain temperature because of the way they sound, so in this case at least there appears to be an auditory component. However, they say that general sounds (non-linguistic) only have very vague or occasional temperature associations, while words with a semantic value, i.e. meaning, are much more likely to feel strongly hot or cold. In this latter case the type of synesthesia should probably not be considered grapheme-temperature, and a term along the lines of lexical-thermal or auditory-thermal could perhaps be invented to describe it. See the page on Music and Temperature for more examples of temperature associations with sounds.

Here are some descriptions written by people with grapheme-temperature synesthesia:


I think of evens as cold and odd numbers as hot.”

(Source: This post on the online debate platform Reddit/Synesthesia. 2020.)

(For other people with this type of synesthesia it can be the other way round: evens are hot and odds are cold).

“From cold to hot: 5 - 7 - 1 - 0 - 3 - 2 - 4 - 8 - 6 - 9.”

(Source: This post on the online debate platform Reddit/Synesthesia. 2020.)

(Here, each digit has a different temperature. Other synesthetes tend to agree that the digit 0 has no temperature, although that isn’t the case for this specific person.)


“O: it’s a cool color, like a deep blue at the bottom of an ocean. (…) E is usually a warm color, like a dirty yellow (a highlighter that's been ruined by another color). (…)

When I was around eight, I developed a kind of system to the (slight) madness occuring in my head.

Words that sounded like E or A, or letters that ended in those sounds were most likely always “warm” colors. Words that ended in O or U or Y and the letters that ended in those sounds were always, always, no matter what, “cool” colors. (…)

It was the same for their personalities. Warm letters were loud, or comforting, motherly and bright. Cool letters were distant, gloomy, quiet, thoughtful.”

(Source: an autobiographical account written by Faithful, a girl with synesthesia. 2019.)

Words… and languages

“I’ve always associated letters and words with temperatures. It has nothing to do with the meaning of a word. For example, ice is a really warm word, tea is cold and January is warm. Some words (like Moon and you) are completely neutral. It’s more about pronunciation than how a letter or a word looks when written down. That said, my letter-temperature associations differ in English and in my native language which is Finnish. In English A is a very cold letter and in Finnish it’s hot and so on.

It also works with languages themselves. Finnish language is lukewarm whereas English is cold. Spanish, Italian, Japanese and Hindi are warm. German and Russian are pretty neutral. French is cold.

However, I don’t seem to associate other sounds with temperatures as strongly as I do with language. If asked I could easily tell if a sound is warm, cold or neutral but it’s not that spontaneous. For example, knocking is a warm sound.”

(Source: This post on the online debate platform Reddit/Synesthesia. 2017.)

Go to the page on grapheme-colour synesthesia

Go to the page on music and temperature

This page last updated: 31 January 2022

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