The English language is a living language with new words entering and leaving the language all the time. In addition, spelling, the use of capitalization, and definitions change over time.
Especially in American English, spelling tends to simplify over time. For instance, the use of the diaeresis has largely been dropped. A diaeresis is two dots that are placed over two vowels to indicate that the two vowels are pronounced separately. Words like coordinate and naive are now generally rendered without the diaeresis, though the forms coöperate and naïve are still sometimes seen. When the transition is complete, the diaeresis will disappear from the typesetter’s repertoire.
Capitalization may also change over time, most commonly affecting words rendered with an initial capital letter changing to a lowercase letter. This usually happens when something that carried a proprietary or brand name becomes so generic that it is no longer only associated with one company. An example of this would be the word taser. Many style guides prefer the capitalized version, Taser, as it is a registered trademark. However, the term has become so ubiquitous, other style guides prefer the lowercase form. The word internet is going through such a change at this time, with some style guides still capitalizing the word and others rendering it with a lowercase i.
The definitions of words may change over time as populations adopt terms that they do not entirely understand. An excellent example of this is the word literally. Literally is an adverb that describes something that is exactly true, something that physically happened. For instance, if someone is literally on fire, he is being physically burned. If someone is figuratively on fire, he is extremely inspired and full of energy. Over the past several decades, many English speakers have not understood this difference. It has been quite common among certain English speakers to use the word literally as an emphasis for the situation they are describing, the word extremely may be substituted for the word literally in these cases. This error has become so widespread the Oxford English Dictionary added this definition of extremely as an informal use of the word literally. As may be expected, precise English speakers the world over were not pleased with this development, however, in a living language it is the common use of words that has precedent over any set of rules.