Start with the intended meaning
Verify the established derivative together with its meaning. Similar bases need not choose the same prefix. A phrase with nicht can also negate an expression, but its focus may differ from a lexical negative adjective.
Recognize negative prefixes without inventing them
klar → unklar / aktiv → inaktiv / materiell → immateriell / legal → illegal / regulär → irregulär Un- is widespread, while in- and its related im-, il-, ir- forms occur especially in established borrowed word families. Their choice is lexical and phonological, not a free menu. The forms im-, il- and ir- reflect adaptation to following sounds in these families. Do not produce “inlesbar” because inaktiv exists; the established word is unlesbar.
A negative derivative may express an opposite or an established evaluation rather than merely negate one occurrence. Unfreundlich is a description of behavior; nicht freundlich can negate that description with a different focus. Some bases have no ordinary negative derivative. When uncertain, a sentence with nicht is often safer than an invented word, but still check its scope.
Apply the pattern in another context
Diese Straße ist mir unbekannt.
Unbekannt is the established negative adjective here. The sentence says that this street is not familiar to the speaker.
Das ist eine inoffizielle Mitteilung.
Inoffiziell is an established word. Its prefix choice does not make in- available for every adjective.
Choose the form and explain the meaning
4. Which existing derivative means not readable: unlesbar or inlesbar?
unlesbar. Negative-prefix choice is lexical, not freely interchangeable.
Additional check 1. Choose the established opposite of möglich: unmöglich or inmöglich?
Unmöglich. Learn the established word; do not select a prefix from a free menu.
Additional check 2. A learner writes infreundlich because inaktiv exists. What is the usual established adjective?
Unfreundlich. The choice is lexical; the existence of inaktiv does not license infreundlich.
Additional check 3. Must unfreundlich and nicht freundlich have exactly the same focus in every context?
No. The derivative can describe an established quality, while nicht can negate a selected description. Context decides how close the readings are.
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German noun compounds: find the head and meaning · Find another grammar topic
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