I recently received an excellent question from a teacher about twin bases. I'm sharing a slightly edited version of the exchange to help teachers with the process of investigating such questions themselves. 
 
Here is the original question: 

 

Just wanted to check in with you about some words.
 
Persuade and persuasion.
 
Im assuming its a twin base of <suad> and <suas>. Is that correct? Is the theory similar for collision and collide? Is the twin base then <lise> and <lide>? Why does it come from the same root and change spelling? 

 

The way to test for twin suffixes is to look up the Latin root of the word you are looking at, and finding the 2nd and 4th part of that Latin verb to see if it makes sense of what your hypothesis of a twin. I'll show you what I mean...

 

So in this case I looked up <persuade> in Etymonline. That sent me to <persuasion> which brough brought me to this:

 

persuasion (n.) <dictionary.gif>
late 14c., "action of inducing (someone) to believe (something); argument to persuade, inducement," from Old French persuasion (14c.) and directly from Latin persuasionem (nominative persuasio) "a convincing, persuading," noun of action from past participle stem of persuadere "persuade, convince," fromper- "thoroughly, strongly" (see per) + suadere "to urge, persuade," from PIE *swad- "sweet, pleasant" (see sweet (adj.)). Meaning "religious belief, creed" is from 1620s.

 

In that information I found the Latin root 'suadere'. Note that the final <ere> of that Latin root is the Latin suffix 'suad(ere)' which gives me reason to hypothesize the bound base <suade> in English. I find that it is common (but not necessary) for Latin roots ending in <ere> to have that turn into a final, single, silent <e> in English. 

 

Now that I have a latin Root for the word you are asking about I go to the Latdict website (a Latin-English dictionary). 

 

When I type in <suadere> in the search for Latin to English I get the following information:

 

 

Screen Shot 2013-12-19 at 11.00.58 AM

 

 

 

 

And above you see the four parts of the Latin verb presented: suadeo, suadere, suasi, suasus

 

When we have twin bases in English, they go back to the 2nd and 4th parts of the Latin verb. In this case <suad(ere)> and <suas(us)>.

 

From those roots we get the English twin base <suade> / <suase> that can build word sums like:

 

per + suade --> persuade

 

or 

 

per + suase/ + ion --> persuasion.

 

This twin, then carries the underlying denotation 'urge, persuade' according to Etymonline. 

 

If you have the RS Tool Box you will have the old RS theme 5H on Twin Bases. I've seen drafts of the new Tool Box 2 version of that theme. It's great!

 

Hope that helps,

 

Cheers,

 

Pete

 

Post Script...

I shared my response and the original question with the Old Grouch pointing out that I'm actuallly fairly new to feeling confident identifying twin bases on my own, so I wanted to make sure that he could correct any false leads I might have signaled. It turned out my investigation was on track. 

However, the Old Grouch did point out something that is important for most Real Spellers users to pay attention to. He pointed out that all either of us had to do was to make use of the "search function" Matt has set up for us. 

I recommend the "Advanced Search" button. 

I clicked that, and then typed <persuade> in the search engine. 

Go to this link to see all the information already archived in Real Spellers to address this question!

Note, the teacher also asked about the words <collision> and <collide>. Anyone out there want to take that one on with the help of LatDict?

 

 

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