https://guidetojapanese.org/learn/grammar/verbparticles lead me to believe that the に particle should be used with a verb. However I have been reading some sentences that have noun + に + adjective.
For example 彼は動物に優しい would this sentence be grammatically correct even though it has no verbs?
Can all adjectives be used with the に particle in this way?
Adjectives are like verbs, in that they 'inflect', that is, have endings that indicate tense (or aspect), just like verbs. So 優しい should be thought of as '[to be] kind', 優しかった, 'was kind'.
に would only be used where an adjective requires it, and this information can only be found in a dictionary, e.g., 動物に優しい, 'kind to animals'; 詐欺に等しい, 'equivalent to fraud'. Other adjectives might take different particles, with 反対 one can find なになにと反対, alongside なになにに反対, both meaning 'the opposite of something'.
