They’re amazing. I wish these things could be expressed so concisely and consistently in English.
A participle is a word that presents an action as a property or state of something: writing, beaten, closed, etc. In English there are two types of participles: present participles, which are usually formed with the ending -ing (e.g. writing, doing, seeing), and past participles, which are usually formed with the endings -en or -ed (e.g. given, closed, written). In Esperanto, there are six types of participles.
Active Participles
-ant- (happening now)
-int- (already happened)
-ont- (will happen)
Passive Participles
-at- (happening now)
-it- (already happened)
-ot- (will happen)
(Note the similarity to the present, past, and future tense endings -as, -is, -os.)
The active participles describe the state of the person or thing doing the action:
skribanta - writing
skribinta - written
skribonta - going to write
skribanta knabo - a boy who is writing
skribinta knabo - a boy who wrote
Mi estis skribanta. - I was writing.
Ili estos skribantaj. - They will be writing.
Ŝi estis skribonta. - She was going to write.
With the -o ending, we present the person who performs the action:
skribanto - writer (one who writes, or is writing now)
skribinto - one who wrote
skribonto - one who is going to write
Participles can also be used as adverbs:
Skribante li pensis pri ŝi. - While writing, he thought about her.
The passive participles express a quality of the thing, which is affected by the action:
skribata - being written
skribita - been written
skribota - going to be written
skribata letero - a letter which is being written
skribita letero - a letter which has been written
La letero estas skribata de mi. - The letter is being written by me.
La letero estis skribata de ŝi. - The letter was being written by her.
La letero estis skribita de li. - The letter was written by him.