In correct English grammar. Are laughing and yawning contagious or infectious?

Answer 1

We use infectious with laughter.

Who are these "we". I was brought up and educated in England so I still need to know the answer to my original question

We, the speakers of Standard English - that is the literary dialect - say infectious with laughing and contagious with yawning. Either contagious or infectious may of course be used with either noun: they are merely adjectives, after all. It is not a question of grammar but of idiomatic meaning.

Infectious has the sense of a benign behavior, such as a laugh or as smile or an up-beat attitude, tending to spread readily to others or to catch on, as part of its dictionary definition. Contagious has, by definition, much of the same meaning as infectious, but lacks that specific sense of a person's good will spreading to others.

We would use contagious to speak of someone's ill willspreading: contagious grumbling or grousing. As for yawning, it is seen as a symptom of a condition, not a benign behavior, and so contagious is more apt than infectious.

Again, there is no grammatical difference between the two adjectives, only a lexical one.

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People who invoke the term Standard English rarely make clear what they have in mind by it, and tend to slur over the inconvenient ambiguities that are inherent in the term. Sometimes it is used to denote the variety of English prescribed by traditional prescriptive norms, and in this sense it includes rules and usages that many educated speakers don't systematically conform to in their speech or writing, such as the rules for use of who and whom. In recent years, however, the term has more often been used to distinguish the speech and writing of middle-class educated speakers from the speech of other groups and classes, which are termed nonstandard. This is the sense in which the word is used in the usage labels in this dictionary. But it should be borne in mind that when it is used in this way, the term is highly elastic and variable, since what counts as Standard English will depend on both the locality and the particular varieties that Standard English is being contrasted with. A form that is considered standard in one region may be nonstandard in another, and a form that is standard by contrast with one variety (for example the language of inner-city African Americans) may be considered nonstandard by contrast with the usage of middle-class professionals." No matter how it is interpreted, however, Standard English in this sense shouldn't be regarded as being necessarily correct or unexceptionable, since it will include many kinds of language that could be faulted on various grounds, like the language of corporate memos and television advertisements or the conversations of middle-class high-school students. Thus while the term can serve a useful descriptive purpose providing the context makes its meaning clear, it shouldn't be construed as conferring any absolute positive evaluation."