3rd declension adjectives in -ης, ες

Some adjectives, like some nouns, have a stem which ended in εσ-, that is to say they should have an  σ before the normal 3rd declension ending. But the -s is dropped and contraction takes place::

  singular    nom             plural     nom     ες   α neuter  
 gen  ος   gen  ων 
 dat  ι   dat  σι 
 acc  α   acc  ας   α neuter  
 

But they drop that σ and contract the meeting vowels according to the by now well-known pattern:

Stressed Ultima
 ἀληθής, ἀληθές
 genitive should be ἀληθέσος  
 drops the σ
 becomes ἀληθέ-ος
 contracts to ἀληθοῦς
 έ  +  ο  >  οῦ 
 έ  +  ι  >  εῖ 
 έ  +  α  >  ῆ 
 έ  +  ε  >  εῖ 
 έ  +  ω  >  ῶ 
        
Unstressed
 πλήρης, πλήρες
 genitive should be πλήρεσος  
 drops the σ
 becomes πλήρε-ος
 contracts to πλήρους

 ε  +  ο  >  ου 
 ε  +  ι  >  ει 
 ε  +  α  >  η 
 ε  +  ε  >  ει 
 ε  +  ω  >  ω 
 
Only little fly in the ointment: accusative plural ε+ας  should be ης  but it isn't.
Quite often  η is replaced by ει . (cf. you want = βουλεῖ for βουλῇ.)
So nominative and accusative plural are both: -εις 
 
  • As example of unstressed -ης, -ες I've taken: full of  πλήρης, πλῆρες 
    skin full of wine, basket full of grapes, tray (of offerings) full of other goods

  • And as example of stressed -ής, -ές I've taken: true, real  ἀληθής, ἀληθές 
    Declension  lower down  on this page.
     

    Masculine and feminine have exactly the same forms

    singular
    nominative    ὁ  ἀσκὸς οἶνου    πλήρης   (skin full of wine
    genitive   τοῦ  ἀσκοῦ οἶνου  πλήρους   
    dative  τῷ ἀσκῷ οἶνου  πλήρει
    accusative  τὸν  ἀσκὸν οἶνου  πλήρη
    plural
    nominative  οἱ ἀσκοὶ οἶνου  πλήρεις
    genitive  τῶν ἀσκῶν οἶνου  πλήρων
    dative  τοῖς ἀσκοῖς οἶνου  πλήρεσιν
    accusative  τοὺς ἀσκοὺς οἶνου  πλήρεις
     
    Neuter nouns (basket full of grapes)
     
    singular
    nominative τὸ  κανοῦν  βοτρύων   πλῆρες
    genitive  τοῦ  κανοῦ  βοτρύων   πλήρους
    dative  τῷ  κανῷ  βοτρύων   πλήρει
    accusative τὸ  κανοῦν  βοτρύων   πλῆρες
    plural
    nominative  τὰ κανᾶ  βοτρύων   πλήρη
    genitive  τῶν κανῶν  βοτρύων   πλήρων
    dative  τοῖς κανοῖς  βοτρύων   πλήρεσιν
    accusative  τὰ κανᾶ  βοτρύων   πλήρη
     
     

    ἀληθής, ἀληθές : true, real

    singular      plural
          masculine 
     feminine 
        neuter           masculine 
     feminine 
        neuter    
     nom    ἀληθ ής       ἀληθ ές       nom    ἀληθ εῖς       ἀληθ ῆ    
     gen  ἀληθ οῦς    gen  ἀληθ ῶν  
     dat  ἀληθ ῇ    dat  ἀληθ έσιν  
     acc  ἀληθ ῆ       ἀληθ εῖς     acc  ἀληθ ές       ἀληθ ῆ  
     voc  ἀληθ ές       ἀληθ ές     voc  ἀληθ εῖς       ἀληθ ῆ  
     

     

    Some more adjectives with the stress on the end syllable:
    • εὐγενής, εὐγενές well-born, noble
    • εὐμενής, εὐμενές kind, kindly, well-disposed
    • εὐτυχής, εὐτυχές lucky, fortunate, happy; prosperous, successful
    • ἀτυχής, ἀτυχές unfortunate, unhappy
    • δυστυχής, δυστυχές unlucky, unhappy, miserable
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

    Like the English, the Greeks said full of things, i.e. they used the genitive:
    What are the following full of?
    • τὸ κανοῦν πλῆρες βοτρύων 
    • ὁ ἀσκὸς πλήρης οἴνου
    • τὸ σκάφιον πλῆρες ἄλλων ὠνίων (other goods)
    • τὰ κανᾶ πλήρη βοτρύων
    • οἱ ἀσκοὶ πλήρεις οἴνου
    • τὰ σκάφια πλήρη ἄλλων ὠνίων (other goods)