In a category 𝒦
suitable for radical theory, a functor Φ : 𝒦→𝒦 is studied which is associated
with a natural transformation 1𝒦→ Φ in a way which bears a formal
resemblance to the behavior of certain “extension” functors of rings, such as that
which assigns to each A the polynomial ring A[x]: every normal subobject
N → Φ(A) has a “contraction” Nc→ A. For a radical class ℛ in 𝒦 such that
ℛ∗= {A|Φ(A) ∈ℛ} is also radical, some conditions are obtained which imply that
ℛ∗(A) = ℛ(Φ(A))c.