English is a peculiarly inflection-less language - neither verbs nor adjectives change form according to gender, and rarely according to number, which serves to make it easier for speakers of other languages to learn it. The actual peculiarities that trouble most learners of English occur largely in spelling and pronunciation:

I take it you already know

Of tough and bough and cough and dough?

Others may stumble but not you

On hiccough, thorough, laugh and through…

(“Hints on Pronunciation for Foreigners”, attributed to G. B. Shaw)

It’s an established truism that in English there are more exceptions than rules. Most of the peculiarities, or reasons for lack of a coherent system of rules governing the entire language, can be traced back to the diverse influences on, and multi-lingual origins of, English. The vocabulary continues to be open to words from other languages, and the grammar was only standardized after centuries of influx of various linguistic groups into the territory from which the language gets its name. The small but busy island knew a long history of colonization: from Roman occupation in the early ADs, through Anglo-Saxon conquests (West-Germanic language group), Viking incursions (Norse influences- North-Germanic), to the Norman Conquest (Old French dialect Anglo-Norman, where Norman stood for a Germanic origin group of “Norsemen”), and a continuing relationship with European language groups.

It is not as if rules don’t exist; it is just that words borrowed from other languages still change form according to the rules that operate in the original context. Therefore, for example, we have plurals like oxen and brethren, clearly deriving from Old English or Middle English practices. (The fact that rules do exist is borne out by the practice of giving out the language of origin of a word at Spelling Bees to help the contestants spell it.)

Pronunciation - Indo-Germanic language group origins, but so many pervasive influences, from Celtic to Norse to Latinate Romance languages. Approximately three hundred years of French as the court language (from the Norman Conquest in 1066 to 1366, when English replaced French as the language of law) meant many French words were added to the vocabulary - bringing in the infamously impossible French pronunciation - “the French don’t care what they do, actually, as long as they pronounce it properly.” (“Why Can’t the English” from the movie My Fair Lady, 1963). The Romance language French meant the further indirect influence of Latin, which came earlier with the Romans and then with the advent of Christianity c. 700 AD. Shakespeare played very consciously upon the fact that Latinate language was used by verbose scholarly types, and French influenced English by accomplished courtiers.

Through various phases of standardization, Middle English turned into modern English somewhere around the fifteenth century: from phonetic spelling in early English texts, no lexicon of grammar, there came the Great Vowel Shift between middle and modern English. The introduction of printing in 1476 (by William Caxton) meant the standardization to some extent of both spelling and grammar, but since most publishing houses were based in London, the language that came into print was the London dialect.

English includes words from languages as diverse as Finnish (sauna), Japanese (tycoon, kamikaze), and Celtic (coombe). The impact of the Empire was also felt on the language - the vocabulary increased to include words from colonized languages (bazaar, pasha etc). American English is a whole other kettle of fish: ‘There even are places where English completely disappears. ‘Why, in America they haven’t used it for years!’ (My Fair Lady, 1963)

The choice of English as a global language can only partially be explained by the fact that the English empire once encompassed one-third of the world. The ease with which English has become the language of commerce, science and politics may have something to do with its easily adaptable character: the vocabulary expands constantly to accommodate ever expanding horizons of human knowledge. Even as we speak, words like blog and friendly-fire have become common parlance, though my dictionary may refuse to recognize them. It remains a fluid, developing language; from ‘leef’ in Middle English to ‘life’ and further shortening syllables - the great Vowel Shift continues.

References:

• Wikipedia: History of England and History of the English Language.
• Merriam-Webster Online: Origins of English.
• The History of the English Language.

Puneet Kaur Hundal