Linguistic determinism is the idea that language and its structures limit and determine human knowledge or thought, as well as thought processes such as categorization, memory, and perception. The term implies that people who speak different languages as their mother tongues have different thought processes.
Linguistic determinism is the strong form of linguistic relativity (popularly known as the Sapir-Whorf hypothesis), which argues that individuals experience the world based on the structure of the language they habitually use.
Though it played a considerable role historically, linguistic determinism is now discredited among mainstream linguists.
The principle of linguistic relativity (or, in other words, the Sapir-Whorf hypothesis) in its strong deterministic form first found its clear expression in writings of Benjamin Lee Whorf.
The term "Sapir-Whorf hypothesis" is considered a misnomer by linguists and academics, because Edward Sapir and Benjamin Lee Whorf never co-authored any works (although they did work together, Sapir being Whorf's mentor), and never stated their ideas in terms of a hypothesis. The distinction between a weak and a strong version of this hypothesis is also a later invention; Sapir and Whorf never set up such a dichotomy, although often in their writings their views of this relativity principle are phrased in stronger or weaker terms.  The two linguists were nevertheless among the first to formulate the principle of linguistic relativity.
Sapir exercised the idea that language is essential to understanding one's worldview and that difference in language implies a difference in social reality. Though he never directly explored how language affects thought, significant traces of the linguistic relativity principle underlie his perception of language.
Whorf took further and reformulated Sapir's thought in his essay "Science and Linguistics". His take on linguistic relativity was more radical: in Whorf's view, the relationship between language and culture was a deterministic one and language played a crucial role in our perception of reality. Language is what gives the thought its expression and thus shapes it; in other words, thinking is determined by language. In "Science and Linguistics" Whorf stated that:
"It was found that the background linguistic system (in other words, the grammar) of each language [...] is itself the shaper of ideas, the program and guide. [...] We dissect nature along the lines laid down by our native languages.
[...] This fact is very significant for modern science, for it means that no individual is free to describe nature with absolute impartiality [...]. We are thus introduced to a new principle of relativity, which holds that all observers are not led by the same physical evidence to the same pictures of the universe, unless the linguistic backgrounds are similar, or can in some way be calibrated."
According to Whorf, formulation of ideas and thoughts is not a rational independent process but is determined by particular grammar and vocabulary of the language in which these ideas are expressed. The world around is organized and made sense of by us through language.
Whorf's conclusion was largely based upon a close examination and extensive study of the Hopi Indian language. During earlier years, Whorf published a number of essays in which he analyzed various linguistic aspects of Hopi. For example, a work called "An American Indian model of the universe" (1936) explores the implications of the Hopi verb system with regard to conception of space and time.
In the course of his research, Whorf noticed that Hopi and some other languages (Hebrew, Aztec and Maya) were built on a different plan from that of English and many other languages which he called SAE (Standard Average European) languages. He discovered a number of significant features differentiating Hopi from SAE languages that led him to the idea of linguistic determinism.
For example, Hopi is a 'timeless' language, whose verbal system lacks tenses. Its assessment of time is different from SAE linear temporal view of past, present and future and varies with each observer:
"The timeless Hopi verb does not distinguish between the present, past and future of the event itself but must always indicate what type of validity the speaker intends the statement to have."
Hopi time is non-dimensional and cannot be counted or measured in a way SAE languages measure it, i.e. the Hopi will not say "I stayed six days," but "I left on the sixth day." What is crucial in their perception of time is whether an event can be warranted to have occurred, or to be occurring, or to be expected to occur. Hopi grammatical categories signify view of the world as an ongoing process, where time is not divided into fixed segments so that certain things recur, e.g. minutes, evenings, or days. The linguistic structure of SAE languages, on the other hand, gives its speakers more fixed, objectified and measurable understanding of time and space, where they distinguish between countable and uncountable objects and view time as a linear sequence of past, present, and future.
Whorf argues that this and numerous other differences imply a different way of thinking. Since thought is expressed and transmitted through language, it follows that a differently structured language must shape thought along its lines, thus influencing perception. Consequently, a Hopi speaker who perceives the world through the medium of his language must see reality through the patterns laid down by its linguistic structure.
Other studies supporting the principle of linguistic determinism have shown that people find it easier to recognize and remember shades of colors for which they have a specific name. For example, there are two words in Russian for different shades of blue, and Russian-speakers are faster at discriminating between the shades than are English-speakers.
Linguistic determinism can also be evident in situations where the means of drawing attention to a certain aspect of an experience is language. For example, in French, Spanish or Russian there are two ways to address a person because those languages have two second person pronouns - singular and plural. The choice of the pronoun depends on the relationship between the two people (formal or informal) and the degree of familiarity between them. In this respect, the speaker of any of those languages is always thinking about the relationship when addressing another person and therefore unable to separate those two processes.
Another example is the Daniel Everett study analyzing conception of numbers in the Brazilian Pirahã people. These individuals could not conceive numbers beyond 'one' and 'two', for which there are no actual terms in their language. After this all numbers are grouped under the term 'many.' Even after being taught in the Portuguese language for eight months, not one individual could count to ten.
However, linguistic determinism has been widely criticized for its absolutism and refuted by linguists. For instance, Michael Frank et. al continued Daniel Everett's research and ran further experiments on the Pirahã published in "Numbers as a cognitive technology," and found that Everett was wrong, the Pirahã did not have words for "one," or "two," but instead had words for "small," "somewhat larger," and "many."
Another argument against the principle of linguistic determinism is that humans are able to perceive objects and events that have no corresponding words in our mental lexicon, even if existing linguistic representations would make the perception easier. Opponents of the theory maintain that thought exists prior to any conception of language. Steven Pinker's theory embodies this idea. He proposed that all individuals are first capable of a "universal mentalese", of which all thought is composed prior to its linguistic form. Language then enables us to articulate these already existing thoughts into words and linguistic concepts.
For example, one may perceive different colors even while missing a particular word for each shade, like New Guinea aborigines can distinguish between the colors green and blue even though they have only one lexical entry to describe both colors. In communities where language does not exist to describe color it does not mean the concept is void - rather the community may have a description or unique phrase to determine the concept. Everett describes his research into the Pirahã tribe who use language to describe color concepts in a different way to English speakers: "[...] each word for color in Pirahã was actually a phrase. For example, biísai did not mean simply 'red'. It was a phrase that meant 'it is like blood'." 
Thus, in its strong version 'Whorfian hypothesis' of linguistic determination of cognition has been refuted. In its weaker form, however, the proposal that language influences our thinking has frequently been discussed and studied.
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Linguistic determinism is a partial assumption behind a number of recent[when?] developments in rhetoric and literary theory. For example, French philosopher Jacques Derrida's dissected the terms of "paradigmatic" hierarchies (in language structures, some words exist only with antonyms, such as light/dark, and others exist only with relation to other terms, such as father/son and mother/daughter; Derrida targeted the latter). He believed that if one breaks apart the hidden hierarchies in language terms, one can open up a "lacuna" in understanding, an "aporia," and free the mind of the reader/critic. Similarly, Michel Foucault's New Historicism theory posits that there is a quasi-linguistic structure present in any age, a metaphor around which all things that can be understood are organized. This "episteme" determines the questions that people can ask and the answers they can receive. The episteme changes historically: as material conditions change, so the mental tropes change, and vice versa. When ages move into new epistemes, the science, religion, and art of the past age look absurd. Some Neo-Marxist historians[who?] have similarly looked at culture as permanently encoded in a language that changes with the material conditions. As the environment changes, so too do the language constructs.
The possibility of linguistic determinism has been explored by a variety of authors, mostly in science fiction. There exist some languages, like Loglan, Ithkuil and Toki Pona for instance, which have been constructed for the purpose of testing the assumption. However, no formal tests appear to have been done.