Problem: Background: David Kellogg Lewis (September 28, 1941 - October 14, 2001) was an American philosopher. Lewis taught briefly at UCLA and then at Princeton from 1970 until his death. He is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years. He made contributions in philosophy of language, philosophy of mind, philosophy of probability, metaphysics, epistemology, philosophical logic, and aesthetics.
Context: Lewis went on to publish Counterfactuals (1973), which contained an analysis of Counterfactual conditionals in terms of the theory of possible worlds. He had already proposed it in some of his earlier papers: "Counterpart Theory and Quantified Modal Logic" (1968), "Anselm and Actuality" (1970), and "Counterparts of Persons and their Bodies" (1971). In spite of significant technical advantages promised by this approach, the theory was widely considered to be too implausible to be taken literally, as Lewis urged it should be. Most often the idea that there exists an infinite number of causally isolated universes, each as real as our own but different from it in some way, and that furthermore that alluding to objects in this universe as necessary in order to explain what makes certain counterfactual statements true but not others, meets with what Lewis calls the "incredulous stare" (Lewis, OPW, 2005, pg. 135-137). Lewis defends and elaborates his theory of extreme modal realism, while insisting that there is nothing extreme about it, in On the Plurality of Worlds (1986). Lewis acknowledges that his theory is contrary to common sense, but believes that its advantages far outweigh this disadvantage, and that therefore we should not be hesitant to pay this price.  According to Lewis, what makes a counterfactual conditional of the form  "Had I made that shot our team would have won the game."  true is that there is a world, as concrete as ours and significantly similar to it, in which my counterpart makes rather than misses the shot and the counterpart of our team wins the game. Had there been a world even more similar to ours in which my counterpart makes the shot but the counterpart of our team still loses the counterfactual would have been false. When we speak of counterfactual possibilities we speak of what is the case in some possible world or worlds. According to Lewis, "actual" is merely an indexical label we give to a world when we locate ourselves in it. Things are necessarily true when they are true in all possible worlds. (Note that Lewis is not the first one to speak of possible worlds in this context. Leibniz and C.I. Lewis, for example, both speak of possible worlds as a way of thinking about possibility and necessity, and some of David Kaplan's early work is on the counterpart theory. Lewis's original suggestion was that all possible worlds are equally concrete, and the world in which we find ourselves is no more real than any other possible world.)
Question: What is modal realism?
Answer: the idea that there exists an infinite number of causally isolated universes, each as real as our own but different from it in some way,

Problem: Background: Benjamin Lee Whorf (; April 24, 1897 - July 26, 1941) was an American linguist and fire prevention engineer. Whorf is widely known as an advocate for the idea that differences between the structures of different languages shape how their speakers perceive and conceptualize the world. This principle has frequently been called the "Sapir-Whorf hypothesis", after him and his mentor Edward Sapir, but Whorf called it the principle of linguistic relativity, because he saw the idea as having implications similar to Einstein's principle of physical relativity. Throughout his life Whorf was a chemical engineer by profession, but as a young man he took up an interest in linguistics.
Context: Whorf's distinction between "overt" (phenotypical) and "covert" (cryptotypical) grammatical categories has become widely influential in linguistics and anthropology. British linguist Michael Halliday wrote about Whorf's notion of the "cryptotype", and the conception of "how grammar models reality", that it would "eventually turn out to be among the major contributions of twentieth century linguistics".  Furthermore, Whorf introduced the concept of the allophone, a word that describes positional phonetic variants of a single superordinate phoneme; in doing so he placed a cornerstone in consolidating early phoneme theory. The term was popularized by G. L. Trager and Bernard Bloch in a 1941 paper on English phonology and went on to become part of standard usage within the American structuralist tradition. Whorf considered allophones to be another example of linguistic relativity. The principle of allophony describes how acoustically different sounds can be treated as reflections of a single phoneme in a language. This sometimes makes the different sound appear similar to native speakers of the language, even to the point that they are unable to distinguish them auditorily without special training. Whorf wrote that: "[allophones] are also relativistic. Objectively, acoustically, and physiologically the allophones of [a] phoneme may be extremely unlike, hence the impossibility of determining what is what. You always have to keep the observer in the picture. What linguistic pattern makes like is like, and what it makes unlike is unlike".(Whorf, 1940)  Central to Whorf's inquiries was the approach later described as metalinguistics by G. L. Trager, who in 1950 published four of Whorf's essays as "Four articles on Metalinguistics". Whorf was crucially interested in the ways in which speakers come to be aware of the language that they use, and become able to describe and analyze language using language itself to do so. Whorf saw that the ability to arrive at progressively more accurate descriptions of the world hinged partly on the ability to construct a metalanguage to describe how language affects experience, and thus to have the ability to calibrate different conceptual schemes. Whorf's endeavors have since been taken up in the development of the study of metalinguistics and metalinguistic awareness, first by Michael Silverstein who published a radical and influential rereading of Whorf in 1979 and subsequently in the field of linguistic anthropology.
Question: What languages and cultures did he helped with?
Answer: