Why did women show their decolletage so much in the past?

In My Humble Opinion
61

[QUOTE=Cervaise]
If I recall correctly, you can get a glimpse of Robin Williams’s taint in a movie from the 80s. The name now escapes me (and I’m too lazy to IMDb it) but it’s the one co-starring Jerry Reed in a wintry setting. Anyway, I clearly recall a scene where Williams is in a hospital bed, wearing a patient gown, and he makes a position-shifting movement which results in a very brief Paris Hilton vehicle beaver. Made quite a retina-searing impression on my young self, I tell you what. Anyway, if you’re interested, I bet you can Netflix it.
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World According to Garp, IIRC.

62

Just read War and Peace, and in a section describing going to the theater comments were made about the amount of bosom women showed (Pierre’s wife Helene, I believe.) That novel was set in the 1st 2 decades of the 19th century.

63

[QUOTE=Risha]
People are often quite surprised to learn how much was allowed at times in the past. During the 1800’s “classical” fashion phase, some upper class women dampened their light and gauzy white dresses (worn with minimal undergarments), to predictable effect.
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I’m having trouble understanding the text. I request visual aids.