Translated as the Greek word for interchange in English, enallage is generally when one particular grammatical element is replaced by another. It can reflect a change of person, such as a substitution of the pronouns you, I, he, or she, or changes in gender, case, or tense. Sometimes enallage is grammatically correct, but often the substitution breaks the basic rules of English. Changes in wording can be made by someone not familiar with the language, or these can be intentional.
The use of enallage is also sometimes to emphasize a point by the speaker or author. A common grammatical substitution in English grammar is to switch pronouns. Someone can refer to the other person as you, for example, but the pronouns he or she may be used instead; this can distract a conversation from being intimate by distancing the other person. The substitution can also be made the opposite way, directing the focus of a conversation toward the other person to make the subject more personal.
Enallage can also involve a switch between active and passive voice. One can directly admit responsibility, but if the pronouns and the wording are changed, then the speaker’s meaning can be totally different. The tense of verbs is often switched with enallage, but this can be deliberate to either make a point or have an effect; such examples include switches between the words was and were, or is and are.
Improper grammar has even been used by popular authors and in books commonly recognized throughout history. Words that are generally not pluralized to indicate more than one can be so, or the change can be grammatically wrong. Authors sometimes write in such ways to create a certain effect, emphasize a point in a quote, or reflect the dialect of a particular character in the story. Grammatical substitution is often accepted in the speech of well-known characters throughout literary history. Similar types of enallage have also often been used in public statements by sports professionals as well as politicians.
A deliberate enallage is often called a figure of speech. Common forms of it may be recognized, but in uncommon variations, or if one makes a mistake in speech, others may perceive the saying as grammatically wrong. There are also more specific forms of misusing English grammar, which relate to ignorance, more specific substitutions of gender or mood, or the substitution of one particular type of speech for another.