I have used the term "quickening" in my blog postings about life beginning at conception. I see that Senator Biden is glomming onto that term but using one specific ancient unscientific definition of it. So lest my readers be confused, here is the scoop on the word "quickening."
If you look through a microscope at a living cell, just before it divides it appears to shake or vibrate. That is "quickening." That is why I use the term to mean that the human sperm fertilizes the human egg, forming a single embryonic cell. That cell moves to the wall of the womb and attaches itself. Once it attaches itself, if it is viable then it does that "quickening" vibration and performs its first cell division. (Living beings grow by a process of continuing cell division.) So what I have explained to you in the blog is that the moment the embryonic cell performs its first division (its very first "growth"), that is quickening and that is when it receives its soul and its guardian angel.
Now, ancient philosophers did not have access to scientific and biological knowledge that we have today. They would mostly have known about embryos and developing pre born babies via observing miscarriages. No one did dissections or have examples to study of babies developing in womb. So when a woman had an early miscarriage, by the time the baby came out, it looked much like a blob of matter and not an individual to the human eye. Thus some philosophers developed the theory that at some point in the womb the baby went from "blob" to "human" and that it was at the human appearing formation that it "quickened," meaning vibrating with life from receiving its soul. Do you see what I mean? They were judging, not surprisingly, that when they observed tissue that came out of a woman who miscarried that it does not "look" human yet, therefore it probably was not quickened with a soul.
Remember that these were very pastoral and agricultural societies, knowledgeable in the reproduction of field and farm animals. So if you break open a chicken egg, you see only a white blob where a future chick would develop. So no one today feels bad about having scrambled eggs. But if you looked inside an egg and saw a miniature baby chick attached, that would put people off of wanting to eat eggs for sure, because visually it would clearly be a little chick. So the people of ancient times were used to knowing that animal embryos looked just like blobs early in their life cycle stage. They likewise concluded that when a woman miscarried something that looked like a blob that this was the "prehuman" form of the baby. When a woman miscarried later in term, where it is recognizably a baby, even after being mangled in the course of being miscarried, philosophers logically assumed that at some point in the womb the proto baby blob "quickened" by getting a soul and then started looking human. They didn't know any better and if you think about it, that's not bad for people living two thousand years ago.
More to the point, they recognized that the soul is entered into the pre-born baby, NOT as the baby exits the womb, which is ridiculous, but obviously the attitude of pro abortionists and astrologers today. So the ancients, using the only evidence they had, which is the bloody mass of tissue after a miscarriage, deduced that at some point in the womb the blob "turned into" a human baby with a soul. They then tried to fix number of days and so forth and got into trouble by guessing that baby girls got souls at different months of gestation than boys and so forth. That could also be because they observed more miscarriages with recognizable gender features at different stages of pregnancy, and being philosophers, not scientists, deduced strictly from that anecdotal observation. In their defense that was not a bad attempt and was definitely a pro-life stance from the very beginning of discussion of this topic. No one doubted it was a baby in the womb and that it got its soul in the womb, but based on tissue observation from miscarriage and lacking microscopes and other devices we have today, they did not understand the early developmental stages of an embryo because they could not see it and see its human features.
Plus, philosophers always differentiated between animals and humans by a criterion of "self awareness." Humans are self aware, while animals are not, they assume. Thus they would think, using their deductive reasoning of the time, that a human baby would not "quicken" and have a soul until it looked like a human, that is, in their mind, that it had the features to be self aware (eyes, ears, fully formed limbs). Again, they would miss evidence of that in the early months of pregnancy because it would be "unclean" tissue that came out during an early pregnancy miscarriage, and not a recognizable human form, as it would be if they could see the scans that we can see today. Also, obviously there is a flaw in their logic that a human gets a soul only when it has the physique to be self aware. God does not wait to give a baby a soul until it has eyes, for example. So they missed that error in their own deductive reasoning process simply because they lacked a view inside the living womb in the earliest days of pregnancy.
I hope this helps.
Oh, by the way, here is another example of quickening that will help in your understanding of medicine. If you ever had an infection you know that an infection hurts. Well, why does an infection hurt? Infection is caused by bacteria which multiplies very rapidly (in terms of minutes and hours). Bacteria "quickens," that is, vibrates as it goes through this rapid cell division process. This applies pressure and heat to nerves, which is why the pain is rapid and acute. Some infections, gross as this sounds, you can feel the vibration of the bacteria growing (yuck). I have felt it and if you ever had "red eye" (conjunctivitis) you probably felt it too, times when your eye vibrates from the infection. That's the bacteria actually "quickening" and growing (yuck). An anti-biotic does not kill bacteria. An anti-biotic stops the bacteria from multiplying, so with the very short life span of bacteria cells they die out and are not replaced by new bacteria. That is how eyedrops work against conjunctivitis; the drops are not killing the bacteria but prevent them from reproducing and thus you wait until all the bacteria dies in the course of its natural short life span of days or at most weeks.
This is also why when one takes an anti-biotic in pill form, one must keep taking all the pills even after the symptoms are gone. This is because like I said, the anti-biotic does not kill the bacteria; it prevents it from reproducing. Thus you might have some bacteria that is still able to reproduce that take longer to naturally die off. You want to keep blocking its ability to reproduce until it does all die off on its own. And that is also why excessive prescribing of anti-biotics can (and already has) result in bacteria that evolve to continue to reproduce even when hit with that particular anti-biotic. That is called "resistence." But that is beside the point, I just thought as part of my series in helping people regain logic and factual information skills that I would provide an example of why the term "quickening" as in vibration came into use and how it is possible to feel it, albeit in a yucky infection experience. Yuck. I could really have skipped those feelings, like bacteria Frankenstein "It's alive." Very yuck.