Breakdown of kokuban ga yogoretara, keshigomu de keseba kirei ni naru.
がga
subject particle
でde
means particle
なるnaru
to become
〜ば〜ba
conditional form
Questions & Answers about kokuban ga yogoretara, keshigomu de keseba kirei ni naru.
Why do we use が after 黒板 instead of は?
が marks the subject that undergoes the action or change—in this case, the blackboard getting dirty. It presents 黒板 as new or focal information. If you used は, you’d be topicalizing the blackboard (“as for the blackboard…”), which can imply contrast or that the board is already an established topic. Here, が is more neutral for stating the condition.
Why do we use 汚れる instead of 汚す in 汚れたら?
汚れる is an intransitive verb meaning “to become/get dirty,” whereas 汚す is its transitive counterpart meaning “to dirty (something).” We want to express “when the board gets dirty” (it’s in that state), so we use the intransitive 汚れる. If you said 汚したら, it would mean “when someone dirties the board,” changing the nuance.
What does the -たら form (汚れたら) indicate here?
The -たら form expresses a conditional or temporal clause: “when/if.” In 汚れたら, it means “when (or if) the blackboard gets dirty.” It can describe a single future event or a habitual/general truth. Here it sets up a rule: whenever the board is dirty, do the next step.
Why is there で after 消しゴム in 消しゴムで消せば?
The particle で marks 消しゴム as the instrument or means by which the action is done. So 消しゴムで消す literally means “erase with an eraser.”
