Stem Changing Verbs

Question

I understand that some verbs are stem changing. In the example of "e" to "ie" verbs, the last "e" of the stem turns into "ie". This rule seems to be true for verbs like nevar (nieva), but why not verbs like "tener"?

Accepted Answer

Hola Kimberly
There's a fair amount of irregularities in the present tense in Spanish. Unfortunately there is no specific rule for knowing when a verb is irregular in the present or not. With stem-changing verbs, we have verbs that share the same rule, i.e. changing the -e to -ie in all forms except for the nosotros and vosotros forms, but for example there are other verbs like tener, decir or venir that undergo a vowel change but not in the first person (yo), they have another specific pattern that they share and that puts them in the category of both yo-go verbs and stem-changing verbs: TENER: tengo, tienes, tiene, tenemos, tenéis, tienen; DECIR: digo, dices, dice, decimos, decís, dicen; VENIR: vengo, vienes, viene, venimos, venís, vienen.
These three verbs happen to be yo -go verbs, but that doesn't mean that all yo-go verbs are stem-changing verbs (salir is: salgo, sales, sale, salimos, salís, salen - only changes on the yo form).
That means that it's necessary to do some memorising when studying the stem-changing verbs in Spanish. : ))
Saludos 
Inma