| Singular | Plural | |
|---|---|---|
| Nominativ | irrationabile | irrationabilia |
| Genitiv | irrationabilis | irrationabilium, irrationabilum |
| Dativ | irrationabile, irrationabili | irrationabilibus |
| Akkusativ | irrationabile | irrationabilia |
| Ablativ | irrationabile, irrationabili | irrationabilibus |
| Vokativ | irrationabile | irrationabilia |