Summary
People used to say mi kepeken e ilo to mean I am using tools. Now they say mi kepeken ilo. kepeken e is always wrong as a result. But some people are bringing back kepeken e for transitive prepositions, which is fun.
Note
In the History section, I give a brief overview of the historical use of kepeken. My involvement with the Toki Pona community only began in July of 2021, so I was not present for any historical practices of Toki Pona. However, I have seen old lessons and documentation, particularly jan Pije’s course, from prior to pu. As such, I provide everything I know to be true as of today.
If you’d like to see how kepeken was taught as far back as 2006, check here!
History
Prior to Toki Pona: The Language of Good (pu), kepeken had a split history. The word saw many distinct uses, both as a preposition and as a transitive verb. These two uses appeared at different times and in different lessons, but the commonality was that they were both used to mean to use. In other words, the proper use of kepeken was both as a transitive verb and a preposition at various times, but they had the same meaning: using.
Since pu, kepeken has been taught as an exclusive preposition, never being a transitive verb and rarely being used without an object as mi kepeken. pu replaced all the previous ways kepeken was used with exactly one use with one meaning: a preposition meaning using.
Modern use of kepeken has seen a small return to kepeken e in the form of transitive prepositions, but these are rare.
Proper use
The recommended use today is to say mi kepeken ilo, or mi pali e tomo kepeken ilo. kepeken, being a preposition, can appear in a la clause as well. kepeken e is considered an error in all cases, and if it were interpreted with a modern view of Toki Pona, it would read something like applying using to in the same way other transitive verbs do.
As a reference on usage: in a (flimsy) comparison to English, consider the word using: I built a house using tools. Using is not analyzed as a preposition in English, but it serves a similar function of providing secondary information about an action.
A structured argument
pu defines kepeken as a preposition meaning “using”
kepeken also has a content word meaning “usage” which is funky and usually similar to nasin, but works
historically, the transitive verb use of kepeken (kepeken e) also meant using but has been considered a grammatical error since pu was published
If kepeken is used as a transitive verb but with its prepositional meaning, it conflicts with the way all the other prepositions work transitively, since all of the others change when transitive vs prepositional, and for some reason kepeken does not
If kepeken is used as a transitive verb but in the way most other content words work, it has this weird meaning of like “applying usage to …” that mostly doesn’t have a use and mostly confuses people, unless you include transitive prepositional phrases (not to be explored here) in your nasin
There are two justifications for kepeken transitive to mean the same as kepeken preposition: the first is historical use, and the second is the fact that some of the other transitive verbs are also outliers (lukin, wile) in not* applying a property to the object, but describing the state of the subject in relation to an object
this is a shorthand; obviously you can say “mi lukin e ijo la o kama jo e ijo lukin” to mean “when I’m looking at a thing, go get the thing I’m looking at;” but lukin/wile/etc still stand out from the other content words in not commonly being used this way; “mi pakala e ijo” is “i apply pakala to the ijo” and “mi wile e ijo” is “i apply my wanting to the ijo”. shorthand. language hard.
Other Notes
There is some fringe use of kepeken e in the form of transitive prepositions!
Consider: mi kepeken ilo e sina. The core of the sentence is mi kepeken e sina, which would mean I apply using to you. The original has kepeken ilo, using tools. If this is considered, the sentence now reads I apply tool-using to you. In other words, this is a concise way to say I make you use tools.