Once upon a time England was an island pretty close to mainland Europe. At that time, what is today England, Wales, and Scotland (and other places) wasn’t as well formed and had a different language than is used today. In fact, linguistically we’d refer to the language spoken at that time as Old English, which was a lot closer in structure and dialect to Old Dutch, which is a Germanic language (meaning: from the German region). Then the French, who lived right across the English Channel just to the south decided to invade England. Once there, the French aristocracy in league with the remaining English aristocracy, began pushing both French and Latin on the people. French for every day conversations and Latin for official and political and religious communications. Things became a mess.
Eventually, as these things happen, Old English started to make headway into a new form that we, today, refer to as Middle English. This is the English if Shakes* and others and is also the English the King James Bible was translated†. However, in the intervening hundreds of years, as English began to take on a form Victor Hugo would refer to as “French pronounced poorly,” the Germanic structure (SVO) was combined with a lot of French and Latinate¥ and a lot of other borrow-words from French and other places as well as a Latin-Greek naming structure that results in what we experience today as Modern English. This is also the reason why Shakes is so hard to understand.
The French language has an odd way of handling pronunciation of some words. Specifically words that end in an alveolar sound and begin with a different alveolar sound. To keep from confusing people when sounds are dropped, the French started added an N before words that began with an open mouth sound (vowels or alveolars, “a,” “e,” “i,” “o,” and “u”). You can see this in action in a couple of ways, such as ever and never. Not ever becomes never, adding the “N” sound.
Because of the French influence on the English language, there are rules, or maybe a rule, that governs when a becomes an. The switch takes place when the first sound of the word after “a” us an alveolar (a, e, i, o, and u as well as “y” when used as a vowell and “h” when not pronounced§.
What makes alveolars or vowels linguistically special is how they are formed, without obstruction by the tongue, teeth, or lips. Instead, these sounds are formed around an open mouth with the tongue or lips in different positions. Since French is the influencer in pronunciation, we follow the french rule of n in front of an alveolar.
As a result, you get sequences as follows:
You also get words that are similar to other words, with an “n” at the beginning:
When writing in the negation either / or becomes neither / nor. You can also read this as not either and not or. In the same way that tense and number and gender all need to match, so to does negation or the use of “N”.
* — Shakespeare. William Shakespeare, the guy who is credited with writing a lot of plays and sonets, though he didn’t have any formal education. Today, I tend to refer to Shakespeare as Shakes just because I do.
† — In the 1800’s Middle English was referred to as Bible English and was considered a writing style of the time. It’s also why there are a lot of ye’s and yay’s and other odd words like thou and thee and more.
¥ — Latinate in this case means derived from the Latin, which is considered a dead language because it’s not spoken outside of the Roman Catholic Church and science. Technically, it’s not a growing language either, since common use ended so long ago as to really not be worth discussing.
§ — England has a tendency to reverse what English speakers in the United States do with “h”. As a result, depending on who’s authoring what you’re reading, words beginning with “h” can trail (or follow) either a or an.