THE SUFFIX -IĜ-.
232. The suffix -iĝ- is used to form intransitive verbs of an inchoative nature.
a. Inchoative verbs from the roots of intransitive verbs indicate the beginning or coming into existence of the act or condition expressed in the root:
sidiĝi, to become sitting, to sit down, to take a seat.
stariĝi, to become standing, to stand up.
b. Intransitive verbs may be similarly formed from the roots of transitive verbs, and indicate an action of the verb not immediately due to the subject's acting upon itself (as in the case of reflexive verbs, 41) and not caused by any direct agency (as in the case of the passive voice, 169):
La pordo fermiĝas, the door closes (goes shut).
La veturilo moviĝas, the vehicle moves.
La branĉo rompiĝas, the branch breaks.
Grupo da personoj kolektiĝis, a group of persons gathered.
Cf. the examples given and the following sentences in which the same verbal roots are used in the simple form and in the passive voice:
Ni fermas la pordon, we close the door. La pordo estas fermita, the door is (has been) closed.
Oni movas la veturilon, they move the vehicle. La veturilo estas movata, the vehicle is being moved.
Mi rompas la branĉon, I break the branch. La branĉo estas rompita, the branch is (has been) broken.
Li kolektis florojn, he gathered flowers. Floroj estas kolektitaj, flowers have been gathered.
c. Intransitive verbs may similarly be formed from adjectival roots, and indicate the acquiring of the characteristic or quality expressed in the root:
laciĝi, to become tired, to get tired.
varmiĝi, to become warm, to get warm.
maljuniĝi, to become old, to age.