The first sentence of Groundwork I is justly famous as Kant indicates here that the "good will" is the only thing that is good without limitation. After opening with this bold statement he proceeds in the first paragraph to contrast the "good will" with a number of other things that are "good" in order to show that the goodness of these other things is only a limited form of "good". So "good will" is thereby distinguished from goods of talent, goods of temperament and goods of fortune. The distinction between the "good will" and goods of temperament is particularly significant since it indicates that the "good will" is not merely a "virtue" that can be listed alongside other virtues but is something that is over and above anything that could be understood as a "virtue".
After these contrasts have been completed Kant proceeds to distinguish the "good will" from gifts of fortune and the whole she-bang of "happiness" and "well-being". This list of contrasts that fills the first paragraph of Groundwork I is subsequently mitigated slightly in the second paragraph where Kant admits that some qualities are conducive to the "good will" and included under this heading are some of the Aristotelian qualities such as moderation in affects and passions. This partial mitigation indicates the sense in which Kant does see the point in the account of virtue (something that evidently is important in the later Doctrine of Virtue) as is made emphatic when he states that the latter constitute part of the "inner worth" of people. This does not prevent the contrast between these virtues and the "good will" still holding in the sense that the virtues are "conditional" goods, not, like the "good will", unconditional ones.
After distinguishing the "good will" from virtue Kant next contrasts it with considerations of utility and consequences since the "good will" is stated to be something that would be good in itself even were it not able to accomplish anything so long, that is, as it did attempt to (and this enables it to be distinguished from "mere wishing"). It is after this second contrast, however, that the argument takes a different turn as Kant considers the obvious objection that the praise he has given to the "good will" contains something extravagant in it.
In considering this objection the point that Kant includes to test it involves a discussion of "predispositions" (a term that returns in his later work on religion). These "predispositions" are what are at work in an organism and indicate its teleological orientation. What is meant by this is that there is something about the purposes an organism has that suit its nature. The reason these considerations are mentioned are to understand the basis of the presence in a being of reason and a will. Kant's point here is that reason and a will do not appear engineered to ensure the happiness of the one who possesses them. Rather, if the point of reason and the will were to promote "happiness" something would have gone awry since instincts are better at attaining some form of it. So this point is intended to suggest that if reason is something that has sway over the will then the basis of this sway is not to produce "happiness" in the being that has them.
Now these considerations touch even the "arts and sciences" (an indication of Rousseau's influence on Kant). But the basic point of them is to suggest that the practical faculty of reason points to something different from a result based in "happiness" and thus indicates again the ground for thinking that there is something "good" in itself about a will formed by reason. This consideration suggests something of a "content" for the "good will" since it has here been clearly distinguished from the promptings of instinct and concerns with "happiness" in favour of direction by reason alone.
After invoking this point suggesting that considerations of purposes cannot lead one to see the point of reason's effect on the will being other than the production of a pure kind of will Kant next unveils the conception of "duty" as something that contains the idea of the "good will" albeit "under certain subjective limitations and hindrances" (Ak 4: 397). This "containment" of the idea of the "good will" is reminiscent of the general procedure of schematism as the latter involves restriction and realisation of a conception. Restriction is indicated in the reference to "limitations and hindrances" but realisation is also referred to as these restrictions "elevate" the conception of the "good will" and allow it to shine more brightly.
Having mentioned the idea of duty Kant now discusses the conception of acting in accordance with duty and mentions how self-seeking aims can produce action that conforms with duty whilst not being done from duty. This point is then contrasted with those who act for a different reason in conformity with duty, due to the gifts of their temperaments (again repeating the point indicated at the beginning that temperament is a conditional good). Being beneficent is not something that should or could depend for its worth on temperament but is grounded in duty as a sole guide to good character.
Similar considerations are again used to rule out determination of worth by reference to acting with regard to one's own happiness before the next point is raised, namely, that actions done from duty do not have their worth in an aim held in view but only on the "principle of the volition" (Ak 4: 400). This principle of the volition is thus understood in a formal way as everything material has been removed from consideration. The result of this isolation of worth is that duty comes to be seen as including in its conception a form of necessity. The "necessity" in question concerns the way that duty presents itself to us. To act in a way that enables us to say we have done something "from" duty is to act with "respect for the law".
The understanding of this notion of "respect" is by means of the will being grounded in a consciousness of law as a representation that undercuts any form of self-love. So respect is something that is distinct from pathological feeling as it is not imposed on us from without but rather given to us by ourselves in relation to law. To say we "respect" law is to say we allow it to move us for itself alone.
This conception of "respect" requires a sense of the law in question and that is one that is seen purely through a formal representation. The law in question cannot concern anything material since we have already removed any material as a ground of affect upon us. It is after this point has been reached in the argument that Kant decisively introduces the conception of "practical judgment" in relation to "common sense" (or "common human reason"). The "practical judgment" of such a common standpoint is precisely to be understood as operative through the representation of formal law.
An example is introduced to illustrate the notion reached which involves the notion of false promising which is shown to produce a practical contradiction (contradiction in conception). Kant suggests that the case helps to show that the common understanding can be led to the idea of universal formal law by merely being made aware of "its own principle". Furthermore, the philosopher has "no other principle" with which to deal than that of common understanding.
This raises the question of why it is necessary then to invoke philosophy at all. Kant's concluding consideration is that whilst common understanding reaches for the universal formal law in its practical judgment that it nonetheless is caught in a "natural dialectic" in which inclination is at war with the law. The needs and demands of inclination cannot be simply done away with and yet they corrupt the law at its root. In response to this "unnoticed" dialectic that afflicts common understanding there is a need for philosophy in order that the "source" of the principle of judgment that such understanding uses can be brought to light.