Conclusion: Virtue is a human being’s ability to overcome
obstacles and obey his/her duty.
                        
Premises:
1.     
Obeying the moral law is a human’s duty.
a.      
Duty is the concept of self-constraint of free
choice (36/379).
b.     
Man is most free when he cannot oppose duty (39/382).
c.      
Duty is to estimate the worth of one’s actions
not merely according to their legality, but also according to their morality,
because the law does not command internal action, only the maxim of the action
(51/393). 
2.     
A duty of virtue is an end and, at the same
time, a duty (40/383).
a.      
An end is an object of free choice and every
action has an end (42/385).
b.     
To have some end of action is an act of freedom
(42/385).
c.      
The act is a categorical imperative of pure
practical reason and combines the concept of duty to the concept of an end
(42/385).
d.     
Duties of virtue are declared by pure reason
(55/395).
3.     
Cultivation of the will to the purest virtuous
disposition is one’s duty (45/387).
a.      
By raising oneself from the crudity of his
nature to humanity, he can set ends for himself, supply instruction to what is
lacking in his knowledge, and fix mistakes in order to be worthy of the
humanity within him (45/387).
b.     
It makes the law coincide with the incentive of
one’s actions, creating an inner moral practical perfection (45/387).
c.      
It is not happiness, but the preservation of the
integrity of one’s morality, that is the end and at the same time a duty
(46/388).
d.     
The greatest moral perfection to achieve is to
make the law not only a maxim, but also an incentive (51/392).
4.     
Inclinations and feelings are obstacles to duty.
a.      
Strength is the capacity and resolved purpose to
resist a strong but unjust opponent; strength of moral disposition is called
virtue (37/380).
b.     
Impulses of nature are unjust opponents of moral
disposition that man must overcome to obey the law (36/379).
c.      
All strength is known only by the obstacles it
can overcome (53/394).
d.     
Man conquers these inclinations through reason
(37/380).
e.      
Doctrine of Virtue is an autocracy of practical
reason, meaning that there is a consciousness (from the categorical imperative)
of the power to become master of one’s inclinations that oppose the law
(41/383).
f.      
Vices, or unlawful dispositions, are hindrances
created by inclinations (65/405).