What is the difference between Canon 50mm 1.8 and 1.4 among camera lenses?

pu1. 1.8 and 1.4 are aperture values, but the smaller the aperture, the brighter the picture can be, so the price goes up
It seems easy because there is no difference in numbers, but the lower the number, the more difficult it is.
The price goes up

2017-10-30

OK

pu2. 1.4 is because the aperture is small, but if it is small, it can accept a lot of light, and then the picture comes out bright, so it looks much prettier

2017-10-30

OK

pu3. If the aperture is small, it's bright, but it's good to blow away the background

2017-10-30

OK