Sound symbolism
In linguistics, sound symbolism is the resemblance between sound and meaning. It is a form of linguistic iconicity. For example, the English word "ding" may sound similar to the actual sound of a bell. Linguistic sound may be perceived as similar to not only sounds, but also to other sensory properties, such as size, vision, touch, or smell, or abstract domains, such as emotion or value judgment. Such correspondence between linguistic sound and meaning may significantly affect the form of spoken languages. History. Plato and the Cratylus Dialogue. In "Cratylus", Plato has Socrates commenting on the origins and  correctness of various names and words. When Hermogenes asks if he can provide another hypothesis on how signs come into being (his own is simply 'convention'), Socrates initially suggests that they fit their referents in virtue of the sounds they are made of: However, faced by an overwhelming number of counterexamples given by Hermogenes, Socrates has to admit that "my first notions of original names are truly wild and ridiculous". Upanishads. The Upanishads and Vyākaraṇa contain a lot of material about sound symbolism, for instance: The concept of Sphota and Nirukta is also based on this. Shingon Buddhism. Kūkai, the  founder of Shingon, wrote his "Sound, word, reality" in the 9th century which relates all sounds to the voice of the Dharmakaya Buddha. Early Western phonosemantics. The idea of phonosemantics was sporadically discussed during the Middle Ages and the Renaissance. In 1690, Locke wrote against the idea in "An Essay Concerning Human Understanding". His argument was that if there were any connection between sounds and ideas, then we would all be speaking the same language, but this is an over-generalisation. Leibniz's book "New Essays on Human Understanding" published in 1765 contains a point by point critique of Locke 's essay. Leibniz picks up on the generalization used by Locke and adopts a less rigid approach: clearly there is no perfect correspondence between words and things, but neither is the relationship completely arbitrary, although he seems vague about what that relationship might be. Modern linguistics. Modern linguistics has been seen as opposing sound symbolism, beginning with Ferdinand de Saussure (1857–1913), considered the founder of modern 'scientific' linguistics. Central to what de Saussure says about words are two related statements: First, he says that "the sign is arbitrary". He considers the words that we use to indicate things and concepts  could be any words – they are essentially just a consensus agreed upon by the speakers of a language and have no discernible pattern or relationship to the thing. Second, he says that, because words are arbitrary, they have meaning only in relation to other words. A dog is a dog because it is not a cat or a mouse or a horse, etc. These ideas have permeated the study of words since the 19th century. Types. Onomatopoeia. Onomatopoeia refers to words that imitate sounds. Some examples in English are "bow-wow" or "meow", each representing the sound of a dog  or a cat. Ideophone. An ideophone is "a member of an open lexical class of marked words that depict sensory imagery". Unlike onomatopoeia, an ideophone refers to words that depict any sensory domain, such as vision or touch. Examples are Korean "mallang-mallang" 말랑말랑 'soft' and Japanese "kira-kira" キラキラ 'shiny'. Ideophones are heavily present in many African and East/Southeast Asian languages, such as Japanese, Thai, and Xhosa. Their form is very often reduplicated, but not necessarily so. Phonaesthemes. A phonaestheme is a sub-morphemic sequence of sounds that are associated to a certain range of meanings. A well -known example is English "gl-", which is present in many words related to light or vision, such as "gleam", "glow", or "glare". Since it is submorphemic, "gl-" itself is not a morpheme, and it does not form compounds with other morphemes: "-eam", "-ow", and "-are" have no meaning of their own. Phonaesthemes, however, are not necessarily iconic, as they may be language-specific and may not iconically resemble the meaning they are associated to. Sound symbolism in basic vocabulary. Blasi et al. (2016), Joo (2020), and Johansson et al. (2020) demonstrated that in the languages around the world, certain concepts  in the basic vocabulary (such as the Swadesh List or the Leipzig-Jakarta list) tend to be represented by words containing certain sounds. Below are some of the phonosemantic associations confirmed by the three studies: Magnitude symbolism. High front vowels, such as /i/, are known to be perceptually associated to small size, whereas low and/or back vowels, such as /u/ or /a/, are usually associated with big size. This phenomenon is known as magnitude symbolism. Sapir (1929) showed that, when asked which of the two tables, named "mil" and "mal", is bigger than the other, many people choose "mal" to  be bigger than "mil". This phenomenon is not only observable in pseudowords, but also present throughout English vocabulary as well. Deictic symbolism. In many languages, the proximal demonstrative pronoun ('this') tends to have high front vowels (such as /i/), whereas the distal demonstrative pronoun ('that') tends to have low and/or back vowels (such as /u/). Examples include: English "this" and "that", French "ceci" and "cela", and Indonesian "ini" and "itu". Pronominal symbolism. First person pronouns ("me") and second person pronouns ("you") tend to contain a nasal sound. Joo (2020) suggests that this may be related to the infant's tendency  of using the nasal sound to seek the attention of the caretaker. Bouba-Kiki effect. Köhler (1929, 1947, 1970) introduced what is known as the Takete-Maluma phenomenon. When presented two shapes, one being curvy and another being spiky, and asked which one is called "Takete" and which one is called "Maluma", participants are more likely to associate the name "Takete" to the spiky shape and the name "Maluma" to the curvy shape. Following Ramachandran and Hubbard (2001), this phenomenon is now more commonly known as the Bouba/kiki effect, and has been demonstrated to be valid across different cultures  and languages. Tactile sound symbolism. Bilabial consonants have been demonstrated to be linked to the perception of softness, arguably due to the soft texture of human lips. The is frequent in words for 'rough' while infrequent in words for 'smooth'. Use in commerce. Sound symbolism is used in commerce for the names of products and even companies themselves. For example, a car company may be interested in how to name their car to make it sound faster or stronger.