It's been my experience that people understand complementary distribution and thus phonemes, in stages. You will feel like you get it, then it will sort of fade away. Later, it will come back. So, be patient. Learning isn't linear: you absorb a little knowledge, forget some, backtrack, restart, and learn more. It's perfectly normal to think you understand this stuff, then get practice problems wrong for a while... before you understand it again.. Be patient. It will come
Think about complementary distribution like this: You have a category of things: each one slightly different from the other, but all related to each other phonetically. Different circumstances require the use of different members of the category to be most appropriate: to sound right.
Let me try out a few metaphors for this concept. If one works for you, use it to help you remember the concept. If it doesn't make sense, ignore it.
1. Imagine I have three shirts: a nice formal button-down silk white one, a warm cozy hand knit sweater, and a bright red T-shirt with something just a little bit rude written on it. They are all my shirts; all members of my shirt category. Which one I choose to wear depends on the situation or the environment if you will. If I am sitting at home on a chilly evening, sipping a cup of tea, I may choose the warm cozy sweater. If the Lord High Chancellor phones up and says he's coming to tea, I'll change to the silk shirt. Afterward, if the local linguists come over and we want to sit by the campfire and play the banjo, I'll put on my red T-shirt. I can't wear my three shirts all at once, and if I choose the wrong one, I'll be in some kind of trouble. the shirts are in complementary distribution.
2. How about a couple zillion molecules of H2o? At room temperature, at room, environment, these manefest as liquid: as water. If I put them in my freezer for a while where the temperture is around 15 degrees, they will manifest as a solid: as ice. If I put them into my tea pot in preparation for making tea for the Lord High chancellor, they will become steam. three instances of the same substance in different conditions showing up slightly differently. Again, complementary distribution.
3. Once upon a time, there was a mild mannered ten year old girl named Becky Botsford. Usually, she goes to school and plays with er pet monkey (Bob) and hangs out with her little brother T J. But, when danger threatens the city, Becky Botsford transforms into WordGirl: a PBS super hero who saves the day. Like Clark Kent and Superman, becky and WordGirl are in complementary distribution.
4. On the other hand, two different superheros contrast. Superman and WordGirl can occur in the same environment. they contrast. They are different.
5. Or, lets' think about ice cream. chocolate sauce and strawberry sauce can both go on your ice cream. No matter where you are, you have the freedom to choose one or the other. choosing one over the other though, makes a difference: a different kind of sundae. Like superman and Wordgirl, they contrast.
6. This is a parenthesis: )
So is this: (
Now if you want to use parentheses, you can, but you should know when and where to use which one. This is correct:
This is not correct:
You know that, to be proper, you have to use this one ( at the beginning of a passage or sequence, and this one ) at the end. To do it otherwise is just wrong. We can say the ( and ) are in complementary distribution: you just can't swap one in for the other. they are two instances of the same kind of thing. On the other hand, < and > are not ( and ). You can take your () out and put <> in their place. ( and < contrast with one another.
Let's move back to linguistics.
Your book has a few things to say about phonemes and allophones in English. Here are two examples for you.
1. There are (at least two kinds of (allophones of) the phoneme p in English. One is aspirated [p] as in 'pit' and 'pat'. a puff of air follows the release of the stop. the second is an unaspirated [p]: the p in spot. Hold your hand in front of your face and say 'pin' and then 'spin'. You might feel more of a puff of air in pin then in spin. These two kinds of /p/ are allophones of the same phoneme in English: one occurs alone before stressed vowels and the other after s for example. If you don't believe that those two kinds of /p/ are different, watch this video taken in our kitchen
[p] is unaspirated following [s]. If you record the word 'spin, then cut off the [s], the [p] will sound odd. It will sound funny word initially without its aspiration. It will not, however, become exactly a [b]: a voiced bilabial stop.
Here is the recorded evidence.
First, the speakers says:
'pin spin' with no modification. Then, the tape is looped and he repeats 'pin spin' except the [s] has been copied from 'spin' and added to the word pin so that you hear s followed by aspirated [p].
Next, the speaker's recording of 'pin spin' is played again but
this time the [s] has been cut off leaving the unaspirated [p] to be word initial. For comparison, the speaker then says 'bin' and the recording of spin without the s is replayed. I'll use a hyphen to denote aspiration here. Click anywhere on the transcribed forms listed below
Every phoneme has to have at least one allophone. You never ever hear a phoneme per se since phonemes are categories of sounds rather than sounds themselves.
Another example of allophones in english is the two kinds of /l/ in midwest English. For most people who speak midwest english, the l sound in leaf is differen from the l sound infeel. Listen here as I pronounce leaf and feel. Then, I will make a swap, taking the l from leaf and putting it at the end of a word and the l in feel and putting in at the beginning. listen!"
The l in leaf is called a 'light l'. the l in feel is called a 'dark l'. Light l's are made by placing the tongue more or less on the alveolar ridge. Dark l's are made by lifting the back of the tongue up toward the velum. These dark l's occur in my dialect only at the ends of words.
In case that doesn't convince you that the two [l] sounds differ, try this: here is the word leaf. it begins with a light (alveolar) [l]. Now, here is the same word literally played backward. It sounds funny because the allophone of [l] that you expect in English word-finally is the dark [l] but you are hearing a light l.
For some people, like Ira Glass of national Public Radio (just to pick an example() the dark l seems to be the only l. Listen to Ira Glass here
One of the characteristics of stereotypical Russian accented English is the use of dark l word initially. Listen
Finally, remember that phonemes are categories of sounds. native speakers recognize the difference between categories but have a tough time distinguishing between allophones of the same phoneme; that is, telling the difference between sounds within the same category. and these are different in every language. that's why we do phonology problems: to figure out which sound s in a particular language are in the same category and which sounds are members of different categories.