A fetus is the only biological entity whose developmental telos leads toward rationality & autonomy

Kant's second formulation: treat humanity not as a means but as an end.

Even if actually existing autonomy is absent, the fetus is—unlike an object—directed toward possessing such autonomy. 

Analogy: A seed oak tree is not an oak tree, but one cannot deny it is the only ontological entity whose telos is fully oakhood. 

Thus, potentiality plus internal teleology confers on the fetus at least minimal moral status. 

The Argument From Irreversibility 

For Kant, moral responsibility is crucially tied to non-reversible effects affecting rational beings. Terminating potential personhood is metaphysically irreversible: once prevented, the future rational agent cannot come into existence. 

Thus, the maxim: I may eliminate a being whose rational agency has not yet been actualized implies: I am justified in preventing the existence of future rational autonomy. 

Kant holds that rationality & autonomy are the supreme moral values. 

So deliberately preventing its emergence is not morally neutral. 

(Kant’s Deepest Point) 

The moment the being is on the only natural trajectory toward rational self-legislation, then the duty becomes precautionary: If uncertainty exists about whether something is properly a bearer of dignity, one must treat it as if it is. 

We can summarize the Kantian position as follows: rationality and autonomy are the supreme moral ends. 

A fetus is the only biological entity whose essential developmental telos leads toward rational autonomy.

To eliminate it is to prevent the realization of that end. Preventing the existence of a future bearer of moral law cannot be universalized without contradiction. Therefore abortion (except where the mother’s own rational agency is critically threatened) violates the categorical imperative. 

See that the Kantian stance is not sentimental or biologically naïve. It arises logically from: the universality test, the refusal to instrumentalize humanity, the intrinsic teleology built into the concept of humanity as rational nature. 

Important Kantian nuance: A truly Kantian pro-life position does NOT (and cannot) base itself on: theological claims, emotive claims, utilitarian claims, sociological claims. 

Instead, it rests on ONLY one point: A being whose nature is to become rational & autonomous must be treated according to laws that protect rational agency. 

Therefore, even if the fetus is not yet a “person,” it is nevertheless the bearer of developing humanity and must not be destroyed for contingent private ends.