Indeed, a lower nature cannot acquire that which is proper to a higher nature except through the action of the higher nature to which the property belongs. For instance, water cannot be hot except through the action of fire. Now, to see God through His divine essence is proper to the divine nature, for it is the special prerogative of any agent to perform its operation through its own form. So, no intellectual substance [that's us, and the angels - RdP] can see God through His divine essence unless God is the agent of this operation (SCG III, 52, 2).The gulf between God and us is such that we cannot cross it in our own strength. It's not that he is too far away, but that he is infinite and we are not.
Seeing God’s substance transcends the limitations of every created nature; indeed, it is proper for each created intellectual nature to understand according to the manner of its own substance. But divine substance cannot be understood in this way, as we showed above. Therefore, the attainment by a created intellect to the vision of divine substance is not possible except through the action of God, Who transcends all creatures (ibid., 6; emphasis added).Our created powers are simply not capable of seeing God. So we need his help in order to attain the vision of God.
In fact, we have shown that man’s happiness, which is called life everlasting, consists in this divine vision, and we are said to attain it by God’s grace alone, because such a vision exceeds all the capacity of a creature and it is not possible to reach it without divine assistance. Now, when such things happen to a creature, they are attributed to God’s grace. And the Lord says: “I will manifest Myself to him” (John 14:21) [ibid., 7].So we see that those who suggest that Catholics are Pelagian, or semi-Pelagian, or "demi-Pelagian," or "demi-hemi-semi-Pelagian," are either grossly ignorant of the facts, or willfully lie about us. This error, or lie, cannot be sustained on any fair reading of Catholic dogma. Indeed, as St. Thomas makes clear in the Summa Contra Gentiles, it's not merely a doctrinal error but an error of reason to suppose that we can save ourselves: it is irrational. It would be refreshing if anti-Catholics and others could stick to the facts in their complaints about us, rather than making things up like this.
Unfortunately I fear this is unlikely to happen in most cases, particularly for those who think that they are able to judge a Catholic's heart. We see this most often when a Protestant supposes that veneration of Mary is the same as idolatry. It doesn't matter to most such folks that we deny that we worship Mary; they think they know better than we do what we are doing, and so they're perfectly happy to ignore our protest. Such people really aren't worth our time: if they can't admit that they don't know our hearts, and therefore are in no position to judge whether we worship Mary, they certainly aren't honest in their opinions about us.
The same goes for those who falsely say that we believe we are saved by works, no matter how many times we insist that we are saved by God's grace in Christ. If they will not listen to our explanations, they are not honest in their criticisms. Certainly some of those who do such things are simply ignorant, and they may be forgiven their error; but if they persist in it when we have explained ourselves, there really isn't much left to say to them. It's not simply an honest mistake nor an honest disagreement at the point where the critic ignores what we say and paints us with the brush of his choosing.