Consonants use some part of your vocal tract to stop, impair, or redirect the air flowing from your lungs. For instance, when you say ‘t,’ you stop the airflow by touching your tongue to the roof of your mouth just behind your teeth. Say “tub” and you can feel it. If you say “sit” you can feel that the ‘s’ sound is made by raising your tongue near the roof of your mouth and making a hissing sound. When you say “bat” you stop the air with your lips when you make the ‘b.’

The modification of the airflow is called articulation, where the modification takes place is called the place of articulation, and the way that it is modifying the airflow (stopping it, causing it to hiss, letting air through your nose) is called the manner of articulation. Just as vowels can be categorized by frontness, height, and rounding; consonants can be categorized by place and manner of articulation (Place and Manner of Articulation).  

The major categories of consonants I use here are obstruents and vocalic/syllabic.  Vocal and syllabic refer to different properties of the same sounds and are synonyms. I will use syllabic here, which means that they can form the core of a syllable as vowels do. 

Obstruents restrict or stop the airway.   For instance, the ‘b’ sound in “bat” stops the air with your lips. The ‘s’ sound in “sit” restricts the airway to produce a hissing sound. 

There are two other English sounds that do not fit well into either category, ‘y’ and ‘w.’   These are called approxiates, because they restrict the airflow but not enough to cause turbulence as with the obstruents  We have already seen these sounds are part of diphthongs as in “boy” /bɔɪ/ or “cow” /kaʊ/. 

Obstruents are discussed in detail in the section on obstruents, but the 10,000-foot view is that they are divided into three categories, stops, fricatives and affricates  Stops are sounds that completely block the airway, like /t/, or /p/.  Fricatives are sounds that restrict the airflow so that there is a hissing noise, like /s/, and /f/. 

Affricates combine a stop and an affricate.  English has two of them,  the ‘ch’ sound in “chuck” /tʃʌk/ and the ‘j’ sound in “joke” /dʒoʊk/.  The way they are written in the IPA shows what the two sounds are that make each of them up.  The ‘ch‘ is a ‘t‘ sound followed by a ‘sh‘ sound.  The ‘j’ is a ‘d’ sound followed by a ‘zh‘ sound.  However, they are heard as a single phoneme

‘M’ and ‘n’ are called nasals because air flows through your nose when making the sounds.  They can stop the sound entirely as in “make” /meik/ or “next” /nɛkst/.  Or, they can act as vowels, as in “bottom” /bɑɾʔm̥/ and “button” /bʌɾʔn̥/. 

Still another type of syllabic consonant is called a liquid.  In English, these are ‘r’ and ‘l.’  As with /m/ and /n/, these can be obstruents or syllabic.   ‘R’ is an obstruent in “red” /ɹɛd/ but it is syllabic in “bird” /bɝd/ or “butter” /bʌɾɚ/.  ‘L’ is an obstruent in “lead” /lɛd/ but it is syllabic in “bottle” /bɑɾʔl/. 

Consonants have a special place in syllables, preceding or following the vowel that is the syllable core.  In English, it is common to have several consonants in a row in a syllable as in the word “next” /nɛkst/, above. 

As with all sounds, they can be related to each other by similarities. To talk about the similarities, we need to look carefully at the place and manner of articulation of the sounds we are learning.