Crisp summarises the historical consensus on original sin as follows:

1. There was an original pair from whom we are all descended.
2. This pair introduced the morally vitiated condition from which all subsequent humans suffer.
3. All humans after the fall of the original pair possess the condition of original sin and are in need of salvation, without which they will perish.

To these affirmations, Crisp argues, some theologians (especially Augustinian ones) want to add another:

4. All humans after the fall (barring Christ) bear the guilt of Adam’s sin, so that in addition to possessing the condition of original depravity they also bear original guilt.

This fourth notion, he argues, “is not a doctrine universally affirmed and has generated a number of significant problems, as we shall see.” These problems are chiefly the moral, legal and apologetic ones that we all know and love.

So what is the Zwinglian alternative? This:

Zwingli characterised original sin as analogous to an inherited disease or defect that inevitably gives rise to actual sin, for which humans are culpable. Possession of original sin was not itself culpable, Zwingli said, any more than being born a slave is a circumstance for which one is culpable ... Much as a human may be born with the property of being capable of conscious thought, so, on this way of thinking, fallen humans are bearers of a property that means they are morally disordered in some fundamental respect, such that they will inevitably sin on at least one occasion.

This view, Crisp argues, ameliorates the moral, legal and apologetic objections which are brought against the concept of original guilt (which, he argues compellingly, should be marked off as a different doctrine to that of original sin). For instance:

In answer to the immorality objection to the transmission of original sin, the Zwinglian can say that it is not immoral for God to allow Adam to freely choose to commit the primal sin. Nor is it immoral that the consequences of this act are transferred to all his progeny as a spiritual disease, moral defect, and inherited condition on analogy with the inheritance of serious medical conditions that are recessive in nature. This is just the natural outworking of Adam’s primal sin, just as, in a different context, the selling of oneself into slavery is the reason why one’s offspring and their offspring, and so on, are all born into slavery. In a sense, and metaphorically speaking, that is just what Adam has done: he has sold his offspring into a condition of bondage to sin.

In other words, Zwingli (and, following him, Crisp) is not denying the doctrine of original sin at all, but denying that it has to involve original, transmitted or imputed guilt. Food for thought.