Esperanto has most of the verb forms found in western languages, and some more. All forms are regular. The forms used more often are created synthetically using suffixes, the rest is created analytically using auxiliary verb esti – ‘to be’ and participles.

I discuss the simple forms first, then the complex forms. See also suffixes ig and iÄ? in §4.2.2.1 and §4.2.2.2. For detailed information on usage of the verb forms, see PAG §110-119.

Infinitive (infinitivo) is formed from the stem by adding the ending i.
esti – to be, sidi – to sit, kapti – to catch, marteli – to hammer, skribi – to write, bezoni – to need.

Infinitive has the same meaning as in many other languages:
Mi Ä?ojas vin vidi. = Mi Ä?ojas, ke mi vin vidas. – I am happy to see you.
Mi vidis la knabon kuri. = Mi vidis, ke la knabo kuras. – I see the boy running.
Kritiki estas facile, sed fari estas malfacile. – It is easy to criticize, but it is hard to work.
Mi povas legi. – I can read.

All tenses (relative and absolute) are formed uniformly using three vowels:

• a for the present tense, contemporaneous, imperfectness
  mi kaptas – I catch
  kaptanta – catching
  kaptata – being caught
• i for the past tense, anteriority, perfectness
  mi kaptis – I caught
  kaptinta – having caught
  kaptita – having been caught
• o for the future tense, succession, intention
  mi kaptos – I will catch
  kaptonta – going to catching
  kaptota – going to be caught

present	mi kapt-a-s	I catch
past	mi kapt-i-s	I caught
future	mi kapt-o-s	I will catch

Conditional (kondicionalo) is formed by adding the ending us to the stem.
mi kapt-us – I would catch

Imperative (volitivo) is formed by adding the ending u to the stem:
kapt-u – catch
ni kapt-u – let’s catch
Volitive is used also as subjunctive:
Mi petas, ke li venu.^H – I ask that he comes.
Mi deziras al vi, ke vi resaniÄ?u.^H – I wish you to get healthy again.
Mi alportis la libron, por ke vi Ä?in tralegu.^H – I brought the book for you to read.

There are three types of active and three types of passive participles – present, past (perfect) and future (predicative).
Active participle is created from the stem by adding a vowel of tense, followed by nt, followed by adjective ending a.

Passive participle is created from stem by adding a vowel of tense, followed by t, followed by adjective ending a.

Gerunds are formed from participles by replacing the adjective ending a by the adverbial ending e.
Active gerunds:

Promentante ili kantas.^H – Walking, they are singing.
Reveninte hejmen, ŝi komencis legi.^H – Having came home, she started to read.
Pagonte li foriris.^H – He left before paying.

Passive gerunds:

Persekutate ili saltis en riveron.^H – Being persecuted, they jumped into the river.
Kaptite ŝi vane provas liberiÄ?i.^H – Having been caught, she is trying to free herself.
Jam kaptote, li eskapis.^H – Nearly caught, he escaped.

Verbal nouns are formed from participles by replacing the adjective ending a by the noun ending o.
Active verbal nouns:

present	kapt-a-nt-o	the one who is catching
past	kapt-i-nt-o	the one who is having caught
future	kapt-o-nt-o	the one who is going to catch

vojaÄ?anto – one who travels, voyager, lernanto – one who learns, pupil, aŭskultanto – one who listens, listener, abonanto – one who subscribes something, subscriber, vizitanto – one who visits, visitor; mortinto – one who died, the deceased, savonto – one who will save, savior, messiah, parolanto – one who speaks, speaker

Passive verbal nouns:

sendito – one who was sent, messenger, juÄ?oto – one who will be judged

“Verbalized participles” are formed from participles by replacing the adjective ending a by the verbal ending i and using it as a normal verb (of course not forming participle). These forms are quite rare, they are equivalents of complex verbal forms (see §3.8.7 below)
kaptanti = esti kaptanta – to be (in state of being) catching
mi kaptintus = mi estus kaptinta – I would have caught

Complex verbal forms are created using the auxiliary verb esti + participle. This way are expressed secondary active tenses, passive voice, and nuances of conditional and imperative.
These complex forms are not so often used. Very often if you use complex form in English you can use simple form in Esperanto.

Imperfect (Imperfekto) is expressed by the auxiliary verb esti + active present participle.

Imperfect is used when you want to express that the process was occurring in the same time as another process or that the process was continuous.
Li mortis. – He died.
Li estis mortanta. – He was dying.
Imperfect is not so often as English progressive tense, because it is often possible to use nonmarked simple verbal form.

Perfect (perfekto) is expressed by the auxiliary verb esti + active past participle.

Perfect is used when you want to express that the process was already finished before some point in the present, past, or future.

Predicative (predicativo) is expressed by the auxiliary verb esti + active future participle.

Predicative is used when you want to express that the process was going to happen after some point in the present, past, or future. Predicative is very often replaced by modal verbs with infinitive:
Mi estas kaptonta. – I am going to catch.
Mi volas/devas/intencas kapti. – I want to/must/am going to catch.

Complex active infinitives are formed from the infinitive of the auxiliary verb esti + active participle.

More precise forms of conditional or imperative can be expressed by combining of the auxiliary verb esti in simple form conditional/imperative with active participles.
Conditional

Imperative

Passive voice (pasiva voĉo) is expressed by the auxiliary verb esti + passive participle.
Imperfect

Perfect

Predicative

Infinitive

Conditional

Imperative

Passive voice is very often expressed by different, simpler means:
Topic-Focus articulation:
La kato estis persekutata de la hundo. = La katon persekutis la hundo. – The cat was chased by the dog.
General subject:
La cervo estis pafita. = Oni pafis la cervon. – The deer was shot.