The reason behind words like “read” having variable pronunciations is due to the phenomenon known as vowel length alternation in English. In this case, the word “read” changes its pronunciation to differentiate between the present and past tense forms.

In general, the pronunciation of these words can be adjusted based on the context and the tense or form intended. When it comes to adjusting vowel sounds to indicate tense, you can consider the following techniques:

1. Learn the Patterns: Familiarize yourself with common patterns of vowel sound changes in English for different verb forms. Understanding these patterns can help you predict the correct pronunciation.

2. Practice Phonetics: Work on your phonetic skills to differentiate between similar vowel sounds. Practice listening to and producing these sounds to improve your pronunciation accuracy.

3. Use Context: Pay attention to the context in which the word is used, as this can often give clues about the intended pronunciation. Contextual cues from the surrounding words and sentence structure can help guide your pronunciation.

4. Consult Resources: Utilize pronunciation guides, dictionaries, and online resources that provide audio pronunciations to help you learn and practice the correct pronunciation of words with variable sounds.

By incorporating these techniques into your language learning process and practice, you can improve your ability to pronounce words like “read” (present vs. past) correctly, especially when the pronunciation is determined by the context in which the word is used.