An archaism is language that was current at one time, but has passed out of regular use. An archaism can be a word, a phrase, or the use of spelling, letters, or syntax that have passed out of use. Because they are both uncommon and dated, archaisms draw attention to themselves when used in general communication.
Archaisms can be used purposefully or accidentally. Writers of historical novels, as well as historians and film makers, for example, do their best to represent time and culture accurately and avoid unintentional archaisms. Creating a fictional character from times past may require extensive research into and knowledge of archaisms.
An example of a fairly common archaism involving spelling and letters is businesses that include Ye Olde in their name. The word Ye does not actually start with a y, as it may appear; it begins with the letter thorn which has passed out of use. Thorn was a letter used to spell the sound we now spell with the consonant digraph th. Hence, Ye is pronounced as and means the. Olde reflects a spelling from Middle English of the word we now write as old. Businesses may use such archaisms to invoke a mood or atmosphere — as in Ye Olde Tea Shoppe or The Publick Theare; or to convey something about their product — as in Olde Musick and Cokery Books, an Australian firm specializing in sheet music and recipes from the past.
Certain phrases are associated with rituals and traditions, and though they would not be considered current if used in general speech or writing, they continue to be used in the venues or situations in which they are meaningful. For example, phrases such as “thou shalt” and “thou shalt not” are considered archaic in general use, but being part of the common English translation of the Ten Commandments, they continue to be repeated and used in that context without calling attention to themselves. Syntax falls into this category as well. Legal writs characteristically include lists of phrases beginning Whereas, followed by one beginning therefore — an archaic style and structure not typically found elsewhere.
Archaisms can also be put to good use when they are carefully chosen to create irony or humor. One could, for example, mock the triviality of an errand run by saying, “Alas, I must away on my journey betimes. I must traverse the roads, journeying hither and yon in search of . . . muffins.” Used seriously in general discourse, however, archaisms can seem affected or be misunderstood.