Throughout the Reasoning Rhyme posts, I refer to the features of segments. These are the aspects of each consonant or vowel that make it the sound it is. This post and its companion on vowels attempt to explain the basics of feature theory in fairly non-technical language, but I'm afraid they'll remain pretty dry! (Remember that the symbols I use to transcribe sounds can be found here.)
The consonantal features describe the place of articulation, the manner of articulation and whether the consonant is voiced or voiceless. Consonants can differ in place of articulation (e.g., /p/ /t/ /k/), manner (e.g., /t/ /s/ /l/) and voicing (e.g., /z/ /s/or /b/ /p/).
Voicing is perhaps the easiest to explain. A voiced sound is one for which the vocal cords vibrate and a voiceless sound is one for which they don't vibrate. All vowels are voiced, but not all consonants. The example above should make it clear enough: in the two pairs, the voiced consonant comes first.
A consonant's place of articulation is defined by the place in the mouth where the air flow is constricted or stopped and what articulators are making the constriction. The main ones we need to worry about are labial, dental, alveolar, palatal, velar and a couple of variations on them:
The labial consonants are articulated with your lips in the case of /p/, /b/ and /m/ or your lips and upper teeth in the case of /f/ and /v/.
The dental consonants /T/ and /D/ are articulated by the tip of your tongue at the teeth.
The sizeable class of alveolar consonants--/t/, /d/, /s/, /z/, /n/, /l/ and /r/--is pronounced by the tip or blade of the tongue at the little ridge just back from your top teeth, which is called the alveolar ridge.
For the palatal consonants /S/, /Z/ and /j/, your tongue sits up at the roof of your mouth--the hard palate.
The sounds /tS/ and /dZ/--the ones at the start of chip and judge respectively--are known as palatoalveolar consonants because the tip of the tongue sits at the alveolar ridge and the body of the tongue presses up against the roof of the mouth.
The velar consonants /k/, /g/ and /N/ (as well as /x/ for those of us who don't lock our lochs) are pronounced by placing the back of your tongue up against the back of your mouth, which is known as the soft palate or velum.
The sound /w/ (and its voiceless counterpart, the Scots pronunciation of wh) is called labiovelar because it is articulated by rounding the lips and moving the tongue into the position for a velar consonant.
Phew! So that's place of articulation. Manner of articulation is another important aspect of consonantal features. It divides into questions of continuancy and sonority.
Continuancy is all about whether or not there is a continued flow of air through the mouth. If the flow of air is stopped completely, the consonant is called a stop. A stop can be nasal (/m/, /n/ and /N/), simply voiced (/b/, /d/ and /g/) or voiceless (/p/, /t/ and /k/).
There are several kinds of continuants, consonants that have a continuous air flow through the mouth: fricatives, affricates and approximants. In fricatives, the air flow is constricted at the same place as in the corresponding stop. Fricatives can be voiced (/v/, /D/, /z/ and /Z/) or voiceless (/f/, /T/, /s/, /S/ and /x/). The affricates /tS/ and /dZ/ are like a combination of a stop and a fricative in quick succession. Approximants have less of a constriction than fricatives and are voiced. They're almost like vowels, if that makes sense. You might see what I mean when I list them: /w/, /l/, /r/ and /j/. The approximants /l/ and /r/ are very closely related and often called liquids.
Stops, fricatives and affricates can be brought together under the term obstruents to describe the fact that the air flow is obstructed. Another important class is the sonorants. As the name implies, they're rather sonorous. It covers nasal stops, approximants and vowels.
If you're still with me (award yourself a chocolate and/or whisky!) you'll probably have noticed that the classes of sonorants, obstruents and continuants overlap in different ways. In the main posts, you'll see those overlaps in action.
I hope that's helpful. Please comment and let me know whether it clears things up or leaves you confused. I'll do another supplement on vowels, but I think they'll be a bit more straightforward to explain.