Jeremy Taylor wrote:

 ​I don't quite understand you. One important purpose of the sex organs is clearly to procreate. I believe Feser's point is therefore that each time sex takes place we need to be open to procreation. I don't see where procreation in large numbers comes into it. Feser argues that whenever we have sex we cannot pervert the ends of our sexual organs, which means we cannot artificially prevent procreation. This end is very much based in biological - it is about the basic biological telos of our sexual faculties.
 

 

The point is that the perverted faculty argument starts with the final cause of Sex. Therefore, it is important to clearly establish what the final cause is.

For Feser, the foremost final cause of sex is to procreate in large numbers. Moreover, According to Feser, the unitive purpose of Sex comes second to procreation in large numbers. ( An analogy put forward by Feser is that when you eat, you are eating for the nutrition and the pleasure which is there in eating is second in priority)

Now with this final cause for sex comes two problems. First, it is not clear how many children one should have (what counts as large, should it be as much as you can perform the sexual act). Second, it implies that you cannot have sex solely for unitive purposes (you cannot have protected sex).


On the other hand, if you define the final cause of sex to be: Having enough number of children in the right circumstances as the main final cause and also unitive purposes as the secondary final cause . Then once a family has enough children, it will ok for the parents to have protected sex because you have fulfilled the final cause of sex which was defined as having enough number of children. Therefore, the perverted faculty argument has noting to say against protected sex in such families.

Regarding intention: to me sterile couple can only have sex for the purpose of unity. Now it does not follow from perverted faculty argument that the

One small answer before going to bed :D

Check Quora. Doing some mathematics, you can reach to the same formuals given by the person in Quora. I do understand that gravity becomes weaker. But at the same time the velocity of gas molecules also decrease. Remember, that it is force that is reducing the velocity. So even if you decrease the force but have some finite force you are still reducing the velocity. If you look at it this way it would make sense. And one last note is that if the gas molecules do not have velocity they cannot go to vacuum. 

EDIT: Check Quora please, I think the guy made a nice explanation. Here I am giving general picture. There is actually some percentage of the gas molecules leaving the earth but it is very insignificant. I will try to read your post more carefully and completely so I can address all the issues but sorry for my very small and limited answers. Now that I am thinking, I believe you are right in some sense but you must also consider that how much gas is leaving the atmosphere. With qualitative language we cannot arrive at the answer. But according the graph that you put the molecules at high heights still have velocity (because of temperauter) but you must also consider that gas is very diluted there and that height gravity is almost the same at sea level. (90 KM is nothing compared to 6400 km which is the radius of earth)

Jeremy Taylor wrote:

 ​I think the point is that contraceptives and homosexual acts are contrary to the nature of the sex organs - they are perverting a faculty. In Thomistic natural law, if I understand it correctly, you are not permitted to use a faculty against its natural ends (teleology) even for some higher, good purpose. You might be able to not use a faculty - for example, to be celibate; but you can't misuse that faculty - for example, homosexual acts for unitive purposes. ​If understand it correctly, and I may be wrong, there is more or less an holistic nature to natural law. You can't misuse bodily faculties to achieve spiritual or psychological ends.
 

I believe the problem is rooted in the fact that we cannot establish  that the main purpose of sex is procreation in large numbers. If we can establish that then rest of argument seems to be acceptable,


Adding to your comment on disregard of intention by natural law, I would like to say that it  actually shows that natural law is incomplete. Because, for sure the intention of our actions are important and especially if you consider how God judges people. I would say God might even consider the intention more important (e.g. if you donate money so that people praise you, God will not approve your deeds as much as he would when you donate in secret)

seigneur wrote:

Now, I have not read the article/book by Feser, but if by "animals" he really meant animals here (and not human beings), then your objection does not apply. Is it reasonable to ask animals to consider the consequences of overpopulation?
 

Actually the way that Feser argues is that for understanding the final cause of an organ, we first look at the animals having that organ. That will determine the main final cause of that organ. Now since we are rational humans, the rationality will improve or add to the function of the organ. For example, while the eyes in animals are for seeing, for us it also helps us not only t

Sorry for the disorganized answer but I hope it helps you.

For our case, it is safe to assume that vacuum is actually nothing and as we know nothing can do nothing ( nihil fit ex nihilo). Now why does it seem like that vacuum can suck out gas molecules?
Basically gas molecules are moving randomly in all direction. Now if you expose these molecules to vacuum, they will start to fill the vacuum (the vacuum is doing nothing). Why does that happens? because the gas molecules are moving in all direction, one of the direction leads to vacuum so they when move toward this direction, they start to fill the vacuum.
So as it can be seen actually vacuum is not doing anything. It does not have any power or so of its own.

just one small note, the air pressure in a container comes from the collision of the gas molecules with the wall of container and thus the higher the velocity of gas molecules the higher the pressure.

Now let us move to the case of earth atmosphere and let us look at it from a different perspective. The atmosphere of the earth is exposed to vacuum, but why then does it not start to fill the vacuum. Well, for the gas molecules to fill the vacuum, they have to have velocity. However, in order for gas molecules to go space, they have to gain gravitational potential energy by sacrificing their kinetic energy (velocity). Since the gas molecules do not have enough velocity they cannot leave the earth. (this is very similar to the fact whatever you throw toward the sky does not leave the earth and again comes back to you)