Jacqueline Baker is a Grade 7 LA Teacher/Curriculum Coordinator at the Johnny Bright School in Edmonton. I was  lucky enough to get to work with the teachers their last year, and then Jacquie and her colleague Amber Cahill attende the 5-day SWI University Course I got to teach at the University of Alberta in the summer. That course included graduate student, Faculty of Education students and teachers from the community. I hope to be able to share more about the amazing work that came out of the work of the students in the course, but for the moment, I am sharing an email I received from Jacquie. 
Please attend to the detail of the evidence that she includes in her question that leads to her essentially working out the key points of her question all on her own. My response is simply helping her see what she already worked out. Further, as is always the case -- note that the most important aspect of this investigation is not understanding the relationshiop between the specific words investigated. The most important lessons to glean from this story is the scientific process that Jacquie and her students take on their own, and then in the posing of their question. As a result they -- and now any other readers of this story -- are gaining experience of the process of investigating spellings that offer compelling hypotheses that we can then reject if we pay close enough attention to the word sum, and etymology. 
Before you read on -- if you take on the challenge of "spelling-out-loud" the word sums when you get to them, I suspect that you will note a detail that Jacquie and I missed at the beginning. See what happens. Here's her email with my repsonses embedded...
I am trying to make Word Study a regular part of my grade 7 language arts classes. Today we are looking at the word <filtrateas it comes up in a short story we are going to read. I am wondering if I could get your advice/help with it.
We've made four hypothesis as a class and now I need to help the students decide what we have evidence of.
Our hypothesis are:
in + fil+ trate → infiltrate
in + filter + ate → infiltrate
in + filtrate → infiltrate
in + filt + rate → infiltrate
The third one, we know for sure. We can see the word is related to <filter>, but can we break it down as in the second hypothesis? 
Right here you demonstrate your excellent scientific instincts about not going deeper until you have evidence.
(First let me take a brief tangent on a note of terminology. I encourage you to consider the phrase "analyze it further" rather than "break it down". It's important to not think of "breaking" words into morphemes. If I "break" <making> into morphemes I might propose <mak + ing>. But now I have "broken" or "violated the structure" of the base <make>. Analysis of morphological structure is not about breaking -- it's about carefully untangling the underlying morphological elements.  If you investigate the etymology of <analyze> it's orthographic denotation you will find from its root conveys this process far more clearly.)
Now back to your analysis:
There is one detail in your word  you have that is so easy to overlook. In fact overlooked it myself until I dug deeper. But first to the excellent instincts...
in + filter + ate → infiltrate
Because you are confident in the meaning and apparent structural connection, you take this as a coherent word sum. Based on that assumption,  you have essentially concluded that your word sum is valid but that leaves the question -- is it a complete analysis?
This is such a key frame for scientific inquiry that  needs to be celebrated. 
In this way, you give yourself and your students the freedom to try some deeper analyses.  You know that unless you find evidence on that quest for a deeper analysis, you can always just go back to this analysis. That process makes me think of how comfortable I am on a climbing wall to try to reach for handholds that seem just out of reach because I have that rope on. If I didn’t know I had a safe fall back position — I wouldn’t try!
But just to be 100% sure, I’m going to check our assumption that really shares a meaning through its history by going to Etymonline (and I get to enjoy its new format!).  
Screen Shot 2017 10 11 at 11.41.12 AM

We see right here that <filtrate> is related to <infiltrate>.And, when I click on<filtrate> in the related words (I love this new feature of Etymonline!) I get this... 

Screen Shot 2017 10 11 at 11.43.12 AM


So we have clear evidence that <filter> is definitely etymologically related to <infiltrate>. Then you make this key observation when you write this:


I don't know how to explain the <e> before the <r> in <filter> if that is the base.....


Ha ha! You caught it.

If you don’t know how to explain the <e> before the <r> in <filter>, you have just found evidence that you need to reject your first hypothesis that seemed so obvious at first! 

Actually, your 3rd word sum IS NOT coherent.

The left side of your synthetic word sum is like this:

in + filter + ate -->

That could only resolve like this:

in + filter + ate --> *infilterate

This is where spelling-out the word sum as you write it is likely to help you catch your error. It's easy to ignore the <eif you just "read" the structures. But if you spell them, you are more likely to catch these details. 

Regardless, you are again showing great scientific instincts because you are not letting yourself shove that "inconvenient truth" of the <e> under the rug.

And then you offer this!

"...or maybe it is just relate and would be in the circle, but not the word matrix. 

Voila! You have just identified your new safe holding position, no matter what else you discover.

The words <filter> and <infiltrate> are etymological relatives, but you do not yet have evidence that they are morphologically related. When you ask, "would it be in the circle but not the matrix (with <filter>)?" this is what you mean.

This is really advanced scientific thinking about your word investigation that would sneak by so many people.

You then ask...

You should go down this path to investigate, but first, let's see what the word sum for <infiltrate> would be with this new understanding if we analyze the <in-> prefix and <-ate> suffix from what is left.  

in + filtr + ate --> infiltrate

Why not a bound base <filtr> that is etymologically related to a free base <filter>?

If I don't yet have evidence of <filt> as a base, I can just work with <filter> as a base. But since I don't have evidence of an *<-r> suffix, I have to accept <filtr> as an associated base to <filter>. We can understand these words as ones that share a root, but not a base element!  

So for the moment, I’m going to stick with this understanding:

Some word sums for the morphological family of the base element <filter

filter + s —> filters

un + filter + ed —> infiltered


Some word sums of the morphological family of the base element <filtr> 

in + filtr + ate —> infiltrate

filtr + ate/ + ion —> infiltration

These morphological families are etymologically related to each other, but they are distinct orthographic morphological families that occupy distinct matrices.

You could put them (and others that you test with a word sum) in the same “oval” to mark the common etymological family.

For those of you wanting to fix these understandings of morphological families and etymological families I recommend the YouTube video at this link:




And because you've encountered this surprising toggling of the <er> and <r> I suspect it will not be long before you encounter this same dynamic in other words that appear to be morphologically related at the start, but may be best understood as etymological relatives.

Thanks for the brilliant investigation that will help so many -- but espeically you and your students.

Cheers, Pete