How are consonants defined in speech?

Consonants are defined as sounds that are produced by constricting airflow through the vocal tract. This constriction can occur in various ways, such as through complete closure (as in the sounds like /p/, /t/, or /k/), narrowing of the vocal tract (like /s/, /f/), or bringing the vocal cords together (resulting in voiced sounds like /b/, /d/, /g/). This characteristic of constricting airflow differentiates consonants from vowels, which are produced without such significant obstruction, allowing for a more open vocal tract.

The focus on airflow constriction is essential in understanding the articulatory phonetics of speech. In contrast, the other options address aspects that do not accurately capture the identity of consonants. For instance, limiting consonants to only voiced sounds ignores voiceless consonants, which are equally part of this phonetic category. Identifying consonants as syllables that end with a vowel or as levels of speech clarity does not align with the phonetic characteristics that define them, further reinforcing the correctness of the choice that emphasizes airflow constriction.