If both the subject noun (nominative case) and the direct object noun (accusative case) are masculine nouns, then the declensions used on the determiners and/or adjectives clearly indicate which noun is playing which role.
Feminine / Neuter / Plural Nouns
The declensions for feminine, neuter, and plural nouns are identical across nominative / accusative lines, so they are of no help in ciphering which noun is the subject and which is the direct object.
When Declensions Are Ambiguous
In some instances, reason alone makes it clear who is who:
So ein hübsches Kleid hat die Frau noch nie gesehen!
(The woman had never before seen such a beautiful dress!)
Although, in German, we can mention the beautiful dress first, we know just thanks to semantics that it’s the woman looking at the dress and not the dress who is looking at the woman.
When Semantics Are Ambiguous
However, whenever the interaction between the subject and direct object nouns would be just as ambiguous as the matching declensions, we must use rigid word order (subject first, then direct object) to communicate who is who:
Die Frau sieht die Katze. (The woman sees the cat.)
Die Katze sieht die Frau. (The cat sees the woman.)
This ‘word order’ option for distinguishing the nominative from the accusative case is the only option we have in English and should thus seem comfortably familiar!
The Four Cases in German
Specifically and exclusively the nominative case is used for subject nouns –whatever noun is the ‘agent’ in a given sentence.
I’m gifting my son a new car for his 16th birthday.
His new car still has that brand-new-car smell.
We must follow the pilot car through the construction.
The totaled car’s make and model are beyond recognition.
In these Standard Word Order sentences, the subject noun is always the noun that comes first (i.e. ‘I’, ‘his new car’, ‘we’, and ‘the totaled car’s make and model’).
Case Systems: German vs. English
English –as a derivative of the same proto-language that modern German comes from, too– used to have gendered nouns and a case system just like modern German still does.
But no longer!
English nouns are either ‘subjects’ or ‘objects’ (i.e. not ‘subjects’). Thus, English typically uses just two cases: the nominative and the objective, respectively.
However, German has double the number of cases!
German divides the concept of ‘objects’ into 2 subcategories: direct objects (accusative case) and indirect objects (dative case). And then the genitive case is sometimes referred to as for ‘possessive’ objects.
But here’s the rub: English noun case is indicated simply by the position of the nouns (e.g. the subject noun comes first). In contrast, German ‘flags’ the case of each noun using tiny changes (a là der, die, das, den, dem, des) called declensions.
How to learn the finicky declensions of the notoriously challenging German Case System is a huge topic. Learn more here!
Examples of The German Case System
Check out these masculine, feminine, and neuter nouns in the four different cases: