diff --git a/src/Iris/ProofMode/Modalities.lean b/src/Iris/ProofMode/Modalities.lean
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+/-
+Copyright (c) 2025 Markus de Medeiros. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Markus de Medeiros
+-/
+import Iris.BI
+
+namespace Iris.ProofMode
+open Iris.BI
+
+inductive ModalityAction (PROP1 PROP2 : Type u) : Type u where
+| isEmpty   : ModalityAction PROP1 PROP2
+| forall    : PROP1 = PROP2 → (PROP1 → Prop) → ModalityAction PROP1 PROP2
+| transform : (PROP2 → PROP1 → Prop) → ModalityAction PROP1 PROP2
+| clear     : ModalityAction PROP1 PROP2
+| id        : PROP1 = PROP2 → ModalityAction PROP1 PROP2
+
+namespace ModalityAction
+
+variable [BI PROP1] [BI PROP2] (s : ModalityAction PROP1 PROP2)
+
+@[simp]
+def intuitionistic_action_spec (M : PROP1 → PROP2) : Prop :=
+  match s with
+  | .isEmpty => True
+  | .forall Hconv C =>
+      (∀ P, C P → iprop(□ P) ⊢ Hconv ▸ M iprop(□ P)) ∧
+      (∀ P Q, iprop(M P ∧ M Q) ⊢ M iprop(P ∧ Q))
+  | .transform C =>
+      (∀ P Q, C P Q → iprop(□ P) ⊢ M iprop(□ Q)) ∧
+      (∀ P Q, iprop(M P ∧ M Q) ⊢ M iprop(P ∧ Q))
+  | .clear => True
+  | .id H => ∀ P, iprop(□ P) ⊢ M (H ▸ iprop(□ P))
+
+@[simp]
+def spatial_action_spec (M : PROP1 → PROP2) : Prop :=
+  match s with
+  | .isEmpty => True
+  | .forall Hconv C => ∀ P, C P → P ⊢ Hconv ▸ M P
+  | .transform C => ∀ P Q, C P Q → P ⊢ M Q
+  | .clear => ∀ P, Absorbing (M P)
+  | .id Hconv => ∀ P, P ⊢ (Hconv ▸ M P)
+
+end ModalityAction
+
+class IsModal [BI PROP1] [BI PROP2] (M : PROP1 → PROP2)
+    (iaction saction : ModalityAction PROP1 PROP2) where
+  spec_intuitionistic : iaction.intuitionistic_action_spec M
+  spec_spatial : saction.spatial_action_spec M
+  emp : iprop(emp) ⊢ M iprop(emp)
+  mono : ∀ {P Q}, (P ⊢ Q) → M P ⊢ M Q
+  sep : ∀ {P Q}, iprop(M P ∗ M Q) ⊢ M iprop(P ∗ Q)
+
+instance [BI PROP] : IsModal (PROP1 := PROP) id (.id rfl) (.id rfl) := by
+  constructor <;> simp
diff --git a/src/Iris/ProofMode/ModalityInstances.lean b/src/Iris/ProofMode/ModalityInstances.lean
new file mode 100644
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+++ b/src/Iris/ProofMode/ModalityInstances.lean
@@ -0,0 +1,38 @@
+/-
+Copyright (c) 2025 Markus de Medeiros. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Markus de Medeiros
+-/
+import Iris.BI
+import Iris.BI.DerivedLaws
+import Iris.ProofMode.Modalities
+
+namespace Iris.ProofMode
+open Iris.BI
+
+section Modalities
+
+variable [BI PROP]
+
+instance : IsModal (PROP1 := PROP) persistently (.id rfl) .clear where
+  spec_intuitionistic _ := persistent
+  spec_spatial P := persistently_absorbing P
+  emp := persistently_emp_2
+  mono := (persistently_mono ·)
+  sep := persistently_sep_2
+
+instance : IsModal (PROP1 := PROP) affinely (.id rfl) (.forall rfl Affine) where
+  spec_intuitionistic _ := affinely_intro .rfl
+  spec_spatial _ _ := affinely_intro .rfl
+  emp := affinely_intro .rfl
+  mono := (affinely_mono ·)
+  sep := affinely_sep_2
+
+instance : IsModal (PROP1 := PROP) intuitionistically (.id rfl) .isEmpty where
+  spec_intuitionistic _ := intuitionistic
+  spec_spatial := trivial
+  emp := intuitionistic
+  mono := (intuitionistically_mono ·)
+  sep := intuitionistically_sep_2
+
+end Modalities