7.1. Cases and postpositions
Cases are markers of the grammatical roles of nouns. In most European languages, inflection of articles, adjectives, and nouns is used to show cases. English pronouns have three cases: the nominative case, the genitive case (possessive case), and the accusative case (objective case). The nominative case is often used for the subject of sentences, and the accusative case is often used for the object of sentences. For instance, the word they is nominative, the word their is genitive, and the word them is accusative. Since common nouns don't have case markings at all to distinguish grammatical roles, English has become full of prepositions. The grammatical role of a phrase is given by its preposition, so you can change the order of phrases without a chance of misunderstanding. For example, you can say both "It rarely snows in Yokohama" and "In Yokohama, it rarely snows," because the preposition in clearly stands for the place. But English has no prepositions to mark the subject and the object, so it uses the word order to determine them. Generally speaking, the fewer case markers (inflection and adpositions) a language has, the more sensitive the language is to the word order. Chinese is very sensitive to the word order because it doesn't have inflection at all and it has few prepositions.
In Japanese, cases including nominative and accusative are always shown by postpositions. You can easily see grammatical roles because all phrases are explicitly marked. Japanese has no noun inflections like English they, their, and them. Memorizing postpositions is much easier than memorizing noun inflections, because neither nouns nor postpositions change their spellings.
There is no marker for verbs in Japanese, but you can easily spot them because they are always at the end of sentences. That comes from the head-last rule, because a verb is the most important part of a sentence and other phrases including the subject are additional information to the verb.
This sentence means "Cherry blossoms bloomed." Please remember Japanese doesn't care much about the distinctions in English shown by the use (or not use) of the definite article the. The postposition が "ga" is the nominative marker, so the preceding noun さくら "sakura" is the subject of the sentence.
Kana: さくらがさいた。 Romanization: Sa ku ra ga sa i ta . Structure: (noun, cherry blossoms) (nominative marker) (verb, bloomed)
This sentence means "An artist drew a picture." The postposition を "o" is the accusative marker, so the preceding noun え "e" is the object of the sentence. Note that the hiragana を is ancient and used only for the accusative marker. Other than that, "o" is always written with the hiragana お.
Kana: がかがえをいた。 Romanization: Ga ka ga e o ka i ta . Structure: (noun, artist) (nominative marker) (noun, picture) (accusative marker) (verb, drew)
Since cases are given by postpositions, you can change the word order like this:
All you have to do is add appropriate postpositions to nouns and put a verb at the end.
Kana: えをがかがいた。 Romanization: E o ga ka ga ka i ta . Structure: (noun, picture) (accusative marker) (noun, artist) (nominative marker) (verb, drew)