Verbs that have stem changes in the present tense (for example i-ie) change all forms of verb except?

Verbs that have stem changes in the present tense (like *i-ie* or *e-ie*) change all forms of the verb except the infinitive and the present participle.

Here's why:

* Infinitive: The infinitive is the base form of the verb (e.g., *to sleep*, *to write*), and it doesn't conjugate.

* Present Participle: The present participle ends in *-ing* (e.g., *sleeping*, *writing*), and it also doesn't reflect the stem change.

Let's look at an example:

Verb: Dormir (to sleep)

* Infinitive: Dormir

* Present Participle: Durmiendo

* Other Forms: Duermo, duermes, duerme, dormimos, dormís, duermen (all show the *i-ie* stem change)

Important Note: This rule applies to regular stem-changing verbs. Some irregular verbs have their own unique patterns.