Zamenhof:2. Substantives are formed by adding o to the root. For the plural, the letter j must be added to the singular. There are two cases: the nominative and the objective (accusative). The root with the added o is the nominative, the objective adds an n after the o. Other cases are formed by prepositions; thus, the possessive (genitive) by de, “of”; the dative by al, “to”; the instrumental (ablative) by kun, “with”, or other preposition as the sense demands. E.g., root patr, “father”; la patr'o, “the father”; patr'o'n, “father” (objective), de la patr'o, “of the father”, al la patr'o, “to the father”, kun la patr'o, “with the father”; la patro'j, “the fathers”; la patro'j'n, “the fathers” (obj.), por la patr'o'j, “for the fathers”.

Rule number 2 of the 16 in Dr. Esperanto's First Book says that the preposition "kun" is used for the instrumental case (which indicates that a noun is the instrument or means by or with which the subject achieves or accomplishes an action).

I may have been mistaken, but I thought that the preposition that was used for the instrumental was "per". I somehow remember that "kun" was specifically used when "togetherness" was implied.

Can someone please clarify for me the usage for these two prepositions?

Thanks.

In Russian language, the preposition “с” (“kun”, “with”) is used with “творительный падеж” (“instrumental case”). So this rule is a not good translation of the Russian First Book.
Examples:
Vi povas skribi per plumo. = You can write by a pen.
Kun plumo vi povas skribi = With a pen, you can write. ≈ If you have a pen, you can write.
Kun helpo de plumo, vi povas skribi = With the help of a pen, you can write.
La gladiatoro kun glavo batalas kontraŭ la glatiatoro kun tridento = The gladiator with a sword fight against the gladiator with a trident.

sergejm:So this rule is a not good translation of the Russian First Book.

That explains it, a bad translation of the First Book.

Thanks for the examples.

I feel better now.