Human freedom is realised in the adoption of humanity as an end in itself, for the one thing that no-one can be compelled to do by another is to adopt a particular end.
Immanuel Kant, Metaphysics of Morals (1797), Part Two: “Metaphysics of Virtue.”
Image incorporating aquatint silhouette by J.T. Puttrich, 1793. Wellcome Collection. Public Domain Mark