Why does the spelling change when congujating some spanish verbs
eg Medir to measure: Yo mido ?? what happened here e has been replaced by i why has e been replaced with an i?
eg Vestirse: el se viste again what is happening ?? Why has i appeared instead of the missing e.
I know the gerund and endings change according to the person but this has nothing to do with this rule...does it??
I am new to spanish and I think there is a flaw in my basic understanding of the concept behind such occurrences.
I need to understand the reasoning behind this.
Gracias
dok951
3 Answers
These are called "stem changing" verbs. In the present tense, there are three groups of stem-changing verbs:
o > ue (for example, contar)
e > ie (for example, cerrar)
e > i (for example, pedir)
Here are some lessons on this:
There is a case for arguing that irregular verbs do not exist; they only appear to be irregular. The "regular" patterns are just our attempts to make sense out of the system - the compulsion of the rational mind to simplify: the framework of regular verb conjugations in any language is merely a set of descriptive observations, not prescriptive rules.
For example, the English verb, "to give", past tense "gave". Is it really irregular? "Gived" is not easy to say, which is probably why it never existed.
Or why does the infinitive "porrere" not exist in Italian? Because it hard to say and that's why it's "porre" instead. In Spanish, the same verb is "poner", so why is the first person singular "pongo" and not "pono"? My feeling is that "pongo" was a natural evolution of pronunciation which happened because the -ng- sound is made on the palate, much closer to where the -o that follows it gets made at the back of the mouth.
It is only because of alphabetic writing that irregular verbs look much more irregular than they truly are. If we focus on language as primarily an oral form of communication, that puts irregular verbs into their proper perspective - a natural development which facilitates efficiency in speech and euphony in hearing.
They are called irregular verbs. Just like am, is are, etc. change unlike sleep, sleeps, sleeping, etc. the root with sleep stays the same while the be verbs change. It is what it is. Hope this helps and I am sure that the gurus will weigh in on this soon. 
