The most important part of the sentence is the predicate. It determines the grammar of the whole sentence. A predicate is almost like the script of a play. The meaning of the predicate verb decides what actors can appear and what their role indicators should be. Therefore to construct a correct sentence we have to be thoroughly acquainted with the meaning of every verb, and know which actors can or must appear. Most important is knowing the details about subject object and predicative.

Subjectless verbs

Almost every Esperanto verb needs to have a subject, but some verbs don't require that function. They are subjectless:

tagiĝi

A single finite verb suffices to make a complete sentence: Tagiĝis. (The day broke.) Baldaŭ tagiĝos. (Soon it will be daybreak.)

temi

Temi (to be about something, cp temo-theme,subject, topic) does not need a subject but normally takes a pri-adject which shows the topic:Temas pri politiko. (It's about politics.) Verŝajne temos pri ni. (Likely it's about us.) The thing that deals with the topic can, however, appear as the subject: La libro temas pri matematiko. (The book is about mathematics.)

pluvi

Pluvis hieraŭ. (It rained yesterday) Baldaŭ pluvos. (It will rain soon.) If anything else rains down besides rainwater, it appears as the subject:Ĉiuspecaj demandoj pluvis sur ŝin. (All types of questions rained down on her.) Ŝtonoj pluvis sur ilin. (Stones rained down on them.) (The thing that is falling can not appear as the object. You can't say Pluvis ŝtonojn sur ilin.)

Intransitive verbs

Most verbs must have a subject, but many of them can't take an object. These are intransitive verbs.

morti

The subject is the one who lost her life: En la domo de la malgranda Niko mortis lia maljuna avino. (At the house of little Niko, his old grandmother died.)

okazi

The subject is an action or something similar: En tiu urbo ĉiujare okazas foiro.(In that town a fair takes place every year.) Kio okazis? (What took place?) Okazis io grava. (Something important took place.)

danci

The subject is the one who is performing the dance: La gejunuloj kune dancis. (The young people danced together.) Sometimes the name of the dance appears as an object: Mi dancis valson kun li. (I danced a waltz with him.)

Transitive verbs

Many verbs that take a subject will also have an object. These are transitive verbs:

vidi

The subject is that which sees something. The object is that which is being seen: La knabino vidas la domon.(The girl sees the house.) Ĉu vi vidis la akcidenton? (Did you see the accident?)

preni

The subject is the one that instigates the action and takes possession of the object. The object is that which through the action of the subject is being taken: Ŝi prenis teleron el la ŝranko. (She took a plate out of the cupboard.)

helpi

The subject is the helper. The person or thing being helped can be the object: Ili helpis la blindulon. (They helped the blind person.) One can also use an al-adject instead of an object: Eble mi povos helpi al vi.

Descriptive verbs

Descriptive verbs link the description to the subject or the object. That kind of description is called a predicative. In most cases it does not have a role marker.

esti

The subject is that which has a certain quality. The quality appears as a predicative: La domo estas granda. (The house is big.) Mia patro estis ŝoforo. (My father is a chauffeur.)

fariĝi

The subject is that which begins to show a quality. The quality appears as a predicative: La etoso fariĝis bona. (The ambiance became good.) Ili fariĝis ŝtelistoj. (They became thieves.)

opinii

The subject is the one that has the opinion about the quality of something. The object is that which has the quality. The quality itself appears as a predicative of the object: Mia fratino opinias viajn klopodojn vanaj. (My sister thinks that your efforts are in vain.)

IG-verbs

Verbs using the suffix IG are always transitive. They indicate the cause of some result. The subject is always the cause or the instigator. The root or roots before IG show the result.

If the result of the IG-verb is a quality or state (position, identity...), the object is that which receives this quality, state, etc.:

lacigi

The object is the person that becomes tired. La tro multa parolado lacigas lin. (Excessive talking tires him.) La vojaĝo certe vin lacigis. (The trip surely made you tired.) Tiu ĉi medikamento estas bona, sed ĝi lacigas la uzanton. (This medicine is good, but causes the user to become tired.)

edzinigi

The object is the person getting married, ie becomes a wife: Mi edzinigas mian filinon ne kun ia simpla nobelo. (I am not marrying my daughter off to some simple nobel.) Li edzinigis ŝin al si per la edziĝa ringo kontraŭ la volo de ŝia patro.(He married her himself with a wedding ring, against the will of her father.)

With some IG-verbs the result is an intransitive action. In that case the IG-verb is made from another verb which is intransitive. With these IG-verbs the object is the subject of the original verb:

bruligi

The object is that which starts to burn: Post infekta malsano oni ofte bruligas la vestojn de la malsanulo. (After an infectious disease they often have the clothes of the sick person burned.) La suda suno bruligas lian nudan kapon. (The southern sun burned his bare head.)

sidigi

The object is the one being placed into a sitting position: Rapide ŝi prenis la infanon sur la brakojn kaj sidigis ĝin sur siaj genuoj. (Quickly the took the child into her arms and sat it on her knees.) La hundon li residigis sur la keston. (He sat the dog down again onto the box.)

With some IG-verbs the result is a transitive action. In that case and IG-verb was made from a verb that is already transitive. There are two ways of using that kind of IG-verb. The object of the IG-verb can be the subject of the original verb, or the object of the original verb:

sciigi

The object can be the person who discovers something: Ŝi sciigis min pri la novaĵo. (She let me know about the news.) Alternatively the object can be the news item: Ŝi sciigis la novaĵon al mi. (She made the news known to me.)

memorigi

The object can be the one who suddenly remembers something:Tio memorigas min pri mia infaneco. (That reminds me of my childhood.) On the other hand the object can also be the memory: Tio memorigas al mi mian infanecon.(That brings back to me my childhood.)

One cannot use both possibilities at the same time. You can't say:Ŝi sciigis min novaĵon. Nek eblas diri: Tio memorigas min mian infanecon.

IĜ-verbs

Verbs made with the suffix IĜ are always intransitive

Usually IĜ-verbs indicate a transition to a new state. The root or roots before IĜ show the result, the new state. The subject of an ordinary IĜ-verb is that which enters into the new state. The instigator of the transition does not normally appear in the sentence. With IĜ-verbs the instigator is of no interest:

malpuriĝi

The subject is that which becomes dirty:Mia vesto malpuriĝis. (My clothes became dirty.

glaciiĝi

The subject is that which becomes ice or icy: La akvo glaciiĝis. (The water froze.)

edziniĝi

The subject is the the bride:Ĉu vi volas edziniĝi kun mi? (Do you want to become my wife?)

With IĜ-verbs made from transitive verbs we are not dealing with the start of a result or a change of state, but with an action which occurs by itself. Either there is no instigator or we are not interested in a possibly instigator. The subject of an IĜ-verb is the object of the original verb. With these verbs IĜ serves to inverse the sentence functions. This is similar to the passive. However with a true passive the instigator must exist, even if not specifically mentioned.

detruiĝi

The subject is that which is completely damaged or destroyed. Whether someone destroyed it or whether it happened on its own is not shown by the IĜ-verb: Tiu ĉi domo detruiĝis dum la milito.(This house was destroyed during the war.) Ĉiuj miaj planoj detruiĝis. (All my plans were wrecked.) The original verb detrui means "completely destroy, wreck, demolish": La milito detruis la domojn. (The war destroyed the houses.)

ruliĝi

The subject is something which moves turning around itself, or a vehicle which moves, because its wheels turn: La veturilo ruliĝis tre rapide. Ruli (to roll) means "to move something by turning it or its wheels": Rulu nun al mi grandan ŝtonon. (Roll a big stone over to me.) La vendisto rulis sian ĉaron laŭ la strato. (The vendor rolled his cart along the street.)

komenciĝi

The subject is that about whose beginning we are talking:Tiam komenciĝis la milito. (Then the war began.) Lia nomo komenciĝas per "Z". (His name begins with "Z".) Komenci means "to bring about a beginning, to do the first part of something": Ili komencis sian vojaĝon. (They started their trip.) Ŝi komencis paroli. (She started to talk.)