Lenition and why that is your mother's fault

Ease of articulation. Don't worry if you never heard of this, all will be revealed. It's a contentious concept in linguistic circles, but for our purposes it's rather helpful.

And feel free just to jump the explanation - it's a bit long - and go straight to the bit where we tell you how lenition works.

Ever noticed how things get slurred in fast speech? Suddenly whole sounds drop out, change into something else ... sometimes that becomes so established that even orthography will reflect that. The word in-pede had become impede long before it even reached Norman French. And be honest - when was the last time you pronounced in BHS as such rather than im BHS? This is where ease of articulation comes in - you are anticipating the next sound you know is to come and your mouth starts getting into position for that sound long before the preceding one has finished. So sounds next to each other become more alike or drop out, if it just gets too tricky for your mouth.

Funnily enough, this also applies to vowels and consonants. Consonants are (in articulatory terms) tricky bastards with a lot of things having to get shifted around (anything from your lips to your pharynx) and held in place, whereas vowels are relatively simple things - just move your tongue a bit this way or that way and you have it.

So when you speed up your speech and have a consonant between vowels, it tries to become more like a vowel. The first thing it loses is the closure that many consonants have (try saying a p - notice how your lips close up for a moment?), becoming a fricative (an [f] in this case - still a consonant but "easier" to say). There may be many intermediate stages, but eventually the consonant either becomes a vowel or disappears altogether. Prove it? Easy. Look at the word for mother in the Indo-European languages and how it developed from ancient Indo-European to our ancestor languages to the modern day ones - watch out for the t:

mātēr (Indoeuropean)
Celtic	Germanic	Romance	Slavonic	Indic	Other
(C. Celtic)	mōder (C. Germanic)	(Italic)	(C. Slavonic)
māthir (Old Irish)	muoter (Old German)	mātēr (Latin)	mati (Old Slavonic)	mātār (Old Indic)	mētēr (Ancient Greek)
					macer (Tocharian)
	mōdor (Old English)	medre (Old French)
	móðir (Old Norse)
màthair (Gaelic)	Mutter (German)	matri (Sicialian)	matir (Ukrainian)	mātā (Bengali)	metéra (Greek)
máthair (Irish)	muter (Yiddish)	madre (Italian)	mat(ka) (Czech)	mātri (Hindi)	mãte (Latvian)
	moder (Danish)	madre (Castilian)	mati (Croatian)	mātu (Pali)	mótė (Lithuanian)
	muada (Bavarian)	mádre (Sardinian)	matj (Russian)	mādar (Farsi)
	mother (English)	matre (Corsican)	mać (Sorbian)
	móðir (Icelandic)		mat (Russian)
mayragh (Manx)	mor (Norwegian)	mare (Catalan)	mazi (Belorussian)	mor (Pashtu)	mayr (Armenian)
	moer (Frisian)	maire (Occitan)
		mère (French)
		mãe (Portuguese)