5 After these points, also, the apostolic teaching is that the soul, having a substance and life of its own, shall, after its departure from the world, be rewarded according to its deserts, being destined to obtain either an inheritance of eternal life and blessedness, if its actions shall have procured this for it, or to be delivered up to eternal fire and punishments, if the guilt of its crimes shall have brought it down to this: and also, that there is to be a time of resurrection from the dead, when this body, which now “is sown in corruption, shall rise in incorruption,” and that which “is sown in dishonour will rise in glory.” This also is clearly defined in the teaching of the Church, that every rational soul is possessed of free-will and volition; that it has a struggle to maintain with the devil and his angels, and opposing influences, because they strive to burden it with sins; but if we live rightly and wisely, we should endeavour to shake ourselves free of a burden of that kind.
From which it follows, also, that we understand ourselves not to be subject to necessity, so as to be compelled by all means, even against our will, to do either good or evil. For if we are our own masters, some influences perhaps may impel us to sin, and others help us to salvation; we are not forced, however, by any necessity either to act rightly or wrongly, which those persons think is the case who say that the courses and movements of the stars are the cause of human actions, not only of those which take place beyond the influence of the freedom of the will, but also of those which are placed within our own power.
But with respect to the soul, whether it is derived from the seed by a process of traducianism, so that the reason or substance of it may be considered as placed in the seminal particles of the body themselves, or whether it has any other beginning; and this beginning, itself, whether it be by birth or not, or whether bestowed upon the body from without or no, is not distinguished with sufficient clearness in the teaching of the Church.
Source: De Principiis (New Advent)