Root classes: why brosi but kombilo

Action roots and thing roots

The second limit on derivation does not need -um- at all. Every root has a class before any ending touches it: an action (kombi, to comb), a thing (broso, a brush) or a quality (bona, good). The endings always make a grammatical word; what that word means depends on the class:

A comb and a brush sit on the same shelf, but their words were built in opposite directions. The action-root names the tool with -il-; the thing-root names the action with a plain -i:

• Mi kombas miajn harojn per kombilo. - I comb my hair with a comb.
• Mi brosas miajn dentojn. - I brush my teeth.

Nothing on the surface warns you. The dictionary form does: a dictionary lists kombi as a verb and broso as a noun, and that is the fact to carry.

The -o of an action-root names the act or its result, never the tool:

• Mi aĉetis ludilon por la infano. - I bought a toy for the child.

When a thing-root becomes a verb

A thing-root takes -i well only when the thing has one obvious action. A hammer has one job, so marteli is plain: to hammer.

• Li martelis la tutan matenon. - He hammered all morning.

A pencil writes, and skribi already says that, so the usual phrase is skribi per krajono. A table has no single action at all: verb it and nobody knows whether you mean laying it, sitting at it or building it. When a thing-root verb would leave your listener guessing, use a plain verb with per:

• Mi skribis per krajono. - I wrote with a pencil.

Mistakes English speakers make