Hey all,

I just received this great question from a principal at the St. Maur International School in Japan who have just jumped into SWI this Septemeber. Cassie share this great image of the thinking they were doing in class. The text of her email is below.

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Hey Pete,
Things are really taking off here and I am doing a lot of the instruction in Grade 5...fun and scary!
I have a new question, not new for you I am sure, but new for me.
Why do these words change structure in the past tense?
We figured <forgive> and <forgave>....kind of....but help please!
They asked why? why? why? I said...I have no idea...I need to ask for help!
There is a lot I love about this question. First off, this teacher, new to SWI,  did so much work organizing their thinking on the white board with data from spellings that use the expected structures, but then also those that don't behave as expected. The best part of that is that Cassie did that knowing full well she did not "know the answer" to her students question. She did what a scientist does -- she dove into a question that she did NOT understand by collecting data and organizing it in a logical way to see if that data could give them some ideas. Cassie and her students will be in such a better place to consider my response precisely because they did this excellent work organizing their thinking.
Crucially let the fact that she did not understand how to explain these spellings become an excuse to call then "irregular spellings"  the kids have to memorize. I note that in her email, Cassie has gone to great pains (I suspect) to avoid the use of the word "irregular". I love her wording, "Why do these words change structure in the past tense?" What a cool way of thinking of it. 
She also didn't simply ask for help without having a go first! 
I receive questions like this all the time. I literally responded to a similar question in a video conference workshop with a school in Edmonton this afternoon. There is much to learn from this question, but I'm going to just start a path with this post. I hope others will chip in to the discussion with their ideas so that Cassie and her students can gain from a community of learners.
One of the most important potential understandings available to this question has to do with gaining a sense of the fact that English orthography evolves. The spellings we have today have "survived" through a process of adaptation. We have the spellings today that best fit  for the represnetation of the sense and meaning of the words for those who know and speak English. (I encourage you to look up <adaptation> in Etymonline to find the orthographic denotation you find by getting to its Latin root.). Don't worry about getting a deep understanding of what it means that English orthography evolves from this little investigation. But I want to highlight that point as one to keep in mind.
Often my first response to a question like this is that it is important to note that asking why we have <sell>, <sell + ing>, <sell + s> but also <sold> instead of *<selled> it to remind the questioner that although this is an interesting question -- its not actually a spelling question. This is a question about oral English. It is not spelling's fault that we have words like <sold>, <run>, <got> and <gave> that Cassie's class has collected on her board. The spelling system doesn't decide whether or not to add an <-ed> suffix to <sell> to mark the past tense. English speaker grow up in an evironment in which native English speakers just don't say a word that could be spelled *<selled> for the past tense of <sell>. Whether or not we like this process of marking the past tense for these words, we should be clear that it is absurd to "blame" spelling for these surprosing past tenses. 
So Cassie and her Grade 5 students are really asking, how come some words don't just do what most words do when we put them in the past tense? 
Here are some initial thoughts. If you look at the words on this white board, you may notice that these words are all fairly basic everyday words. In fact if we investigated their etymology, I suspect we'll find that usually go back to Old English. That might be an important part of the puzzle.
I'm going to link to a video on "irregular verbs" that has some interesting observations that are very useful. The narrator also says things that I find problematic. First of all, they are accepting this term "irregular" which is clearly a pejorative term. A poor message from this film is that these verbs are somehow "bad" and that it would be "better" if they were "regular". 
I disagree! Once you learn the story behind some of these words, you start to get a sense of how English spelling evolves. The coolest part of the video for me is when we find that some of these words that seem to not be standard to day, actually were following an old convention. It's not that these words have random spellings -- there is always a reason and those reasons can be traced in their history. This is the biggest failure of the video. When you watch it, you'll see that it's not that these words are "irregular" they were following the conventions of the environment in which they were established. The thing is, these words were so common that as other words evolved to take on new conventions for marking past tense, these verbs were so common Engish speakers aparently resisted changing them. They stayed like they were. A far more coherent linguistic term that the video should have used to describe this is that these are refered to as "strong verbs". Verbs like <jumped>,  <played> and <painted> that many would call "regular" are refered to as "weak verbs" in linguistics. They just do what most verbs do. Add a /d/, /t/ or /Id/ to the end of these words and spell it with an <-ed> suffix and you have your past tense.
It is interesting to notice that when we make new verbs (and we do all the time), we don't seem to ever make new "strong verbs". I say "yesterday I Googled" something. I don't say "I gaggled." Someone could have tried to establish a non-standard form, but English speakers who hear or read the present tense verb will just assume that if they were to use it in the past tense, they will just do the standard thing. A person here or there trying to get everyone to say a word they way they want it said is a tough hill to climb! But that's the thing about the "strong verbs" we have. They were so commonly used with earlier conventions that people resisted changing them. It's not that we had <drink> and <drinked> and then we moved away from <drinked> to say <drunk>. It's that the past tense of <drink> never took on this newfangled convention for marking past tense that most the other words did. It's not that these words changed to become "irregular" it is that they didn't change. 
That point is well made in the film. When you see that keep in mind what that makes these "strong verbs" not "irregular". 
There is much more that could be said. And I'm sure a real linguist could find wording that I have used here that is non-optimal. I'm be delighted to have any lack of precisions refined for me! But this may be a good place for me to stop, and Cassie and her class -- and anyone else to follow this trail of thought.
CLICK HERE to see the video I mentioned.