How did Rashi understand the verses? How did R' A. ibn Ezra understand Rashi?

yishputu hem (Exod. 18:26) (according to Rashi, following Onkelos, 'they judge') Rashi writes:

It is like yishpotu (This is the preferred reading of Rashi according to Chumash Torat Chaim, although yishpetu is also noted. From R' A. ibn Ezra's question it appears that he read yishpotu), and similarly lo ta'avuri (Ruth 2:8) is like lo ta'avori, and its [Aramaic] translation is dayenin inun ('they judge'). The earlier verses are in the imperative voice and therefore translated into Aramaic as viydunun ('and they should judge'), yeytun ('they should bring'), yedunun ('they should judge'), while these verses express present activity.

R' A. ibn Ezra comments:

It is like yishpotu with a Shuruk instead of a Cholam; similarly vegam lo ta'avuri mizeh (Ruth 2:8) is like lo ta'avori and [attacking Rashi] R' Shelomo wanted to distinguish between them but did not succeed. We may explain [the difference] by the methods of grammar as follows: We have seen chadelu perazon beyisrael chadellu (Judges 5:7), with the Lamed having a Dagesh because it has an Etnach (a mid-verse pause); harim nazolu (Isa. 63:19) at the end of a verse; and it says tehatelu bo (Job 13:9), for they regarded it as the end of the verse, as the word bo is close to tehatelu and is only one vowel. So too, yishpetu hem (Exod. 18:22) is like yishputu (so why is it not yishputu?). We can answer that the [pausal] strength of Etnach is not as powerful as [the pausal form] of the end of the verse. We find amim tachtecha yipelu (Psalms 45:6), hashem al yeminecha (ibid. 110:5), tov asita im avdecha (ibid. 119:65) (all non-pausal forms at a mid-verse pause), the likeness of which never occurs at the end of a verse.

By explaining some novel details in the rules of the pausal form, R' A. ibn Ezra has established that yishputu is a pausal form. It follows that the meaning of yishputu is the same as that of yishpetu. He reads the second sentence in Rashi as attempting to explain the difference between the two words; hence his attack. Rashi however can be understood differently. The first sentence in Rashi may be understood as saying exactly the same as R' A. ibn Ezra. This, however, raises the question why Onkelos translates these words differently. Rashi, who frequently focuses on Onkelos, then explains the translation of Onkelos according to context. The second sentence in Rashi deals with the verses by way of Onkelos. (In the book Lashon Zahav the reading yishpetu in Rashi is accepted, and a different explanation of Rashi is offered.)

Lamed as the fourth root-letter

ha'arafel (Exod. 20:17) ('fog') R' A. ibn Ezra comments 'a four-lettered root'. R' S. R. Hirsch points out that there are a number of roots which have this form. That is to say, a recognizable three-letter root with Lamed added at the end. His examples are giv'ol related to Gimmel, Bet, Ayin; Kuf, Bet, Ayin; Kuf, Vav, Heh; Gimmel, Vav, Ayin; Gimmel, Vav, Heh; Gimmel, Bet, Alef - all of which connote concentration of matter; barzel (close to Bet, Resh, Zayin; Bet, Resh, Dalet); karsol (Kuf, Resh, Samech - connoting bending); and karmel (close to Chaf, Resh, Mem) (Hirsch Commentary, Exod. 9:31; Levit. 2:14). From his discussion of these words, it appears that R' Hirsch regards the Lamed as indicating a strengthening of an aspect of the three-letter root. Similarly, in our case, Ayin, Resh, Peh connotes lowering and dripping, e.g. ya'arof kamatar (Deut. 32:2) ('drip like rain'). It seems that R' Hirsch sees arafel as being a strong form of moisture.