Words ending in a grammatical marker
The majority of words in Esperanto end in a grammatical ending. An "ending-word" consists of a root (or several roots)+ grammatical ending, e.g.: patr/o, roz/o, sun/o, am/o, kol/tuk/o, san/a, verd/a, hel/ruĝ/a, eg/e, aparten/i, bril/as, est/os, rond/ir/as.
Roots express the most diverse things; animals, people, actions, qualities, abstractions, concrete matters etc. A root can not stand alone as a word, but needs an ending. There are nine word-creating endings: O, A, E, I, AS, IS, OS, US and U. When we add any one of these endings to the root it becomes a word. In principle any root can accept any of the endings: hom/o, hom/a, hom/e, hom/i, hom/as etc., blu/o, blu/a, blu/e, blu/i, blu/as etc., kur/o, kur/a, kur/e, kur/i, kur/as etc.
Some roots are used mainly to form compound words. They are called affixes: EBL, UL, MAL, GE etc.
A particle doesn't require an ending, but appears in the sentence as is. Particles are a limited group of words which present very basic ideas, grammatical relations etc. They are mainly prepositions, e.g. al, de, en; personal pronouns, e.g. mi, vi, ŝi; noun-like particles and adjectival particles, e.g. kiu, tiu, kio, tio, kia, tia, kies, ties, ambaŭ; numerals, e.g. unu, du, tri, dek, cent; coordinating conjunctions, e.g. kaj, aŭ; subordinate conjunctions, e.g. ke, ĉu, se; adverbial particles, e.g.: kie, tie, for, kiam, tiam, baldaŭ, hodiaŭ, kial, tial, kiel, tiel, kiom, tiom, ankaŭ, eĉ, jes, ne; interjections e.g. adiaŭ, bis, ho.
45 of the particles seem to have some kind of grammatical ending, and seem to be compounds, but they are not compounds: tio, tia, kio, kie, iu, iel, ĉiam, ĉiom, nenial, nenies and others. These particles are called correlatives.
A Sentence is a string of words which together express a thought. A sentence element is a word or group of words which acts as a unit in a sentence.
The most important sentence element is the predicate. It is a verb with one of the endings AS, IS, OS, US or U (normally not I): iras, sidis, batos, vidus, pensu etc.
The predicate is the center of the sentence. All other (main) parts of the sentence relate in various ways to the predicate. They have various sentence functions, e.g. subject, object, circumstantial complement, vocative, or predicative.
La junulo legas libron. - The young man is reading a book.
The verb legas is the predicate. La junulo is the subject. Libron is the object. The sentence function of the subject is shown by omission of the role indicator (by the nominative). The sentence function of the object is shown by the accusative ending -N.
Ŝi veturis tutan tagon per sia aŭto. - She travelled all day with her car.
The sentence element tutan tagon is an accusative circumstantial complement which shows how long the action lasted. The sentence element per sia aŭto is a prepositional circumstantial complement, which informs about the means used for the action. The sentence function of the first circumstantial complement is indicated by the accusative ending -N. The sentence function of the second circumstantial complement is the preposition per.
Andreo, ĉu vi renkontis Paŭlon hodiaŭ? - Andrew, did you meet Paul today?
The sentence element Andrew is vocative.
La apartamento de Andreo estas malgranda. - Andrew's apartment is small.
The sentence element malgranda is a predicate adjective. It modifies (describes) the subject la apartamento by means of the predicate verb estas:
A sentence element consists of a main word to which various descriptions can be added:
Andreo loĝas en bela apartamento kun du ĉambroj. - Andrew lives in a beautiful apartment with two rooms.
In the circumstantial complement of location, the noun apartamento is the main word. In addition the circumstantial complement has an adjective, bela, which is an epithet of the main word, and a sentence element kun du ĉambroj, which is a supplement of the noun apartamento. (The subordinate sentence element kun du ĉambroj does not relate directly to the predicate, but is only part of the circumstantial complement en bela apartamento kun du ĉambroj.)