Why can't I decrease table cell margins?

Paragraph formatting: indents (left and/or right), Spacing Before/After.

Hi Suzanne,

I should have mentioned that all of those settings you suggest are set to 0. 

I happened to stumble across a partial answer, yet I would still like your assistance. 

Under Table tools > layout > cell margins, the margins are set to 0.

However, under Table Properties > cell > options > cell margins, the margins are set to 0.16".  Changing the margins settings here can change the margins. In the same dialog, there is a setting for "same as whole table."

However, I have gone back and forth with all of these settings and have to say that I am still not clear how they all work together.  Sometimes the setting under Table Tools seems to override the setting under Table Properties. Sometimes it appears to be the opposite.

I am also unclear about what "same as whole table" (under Table Properties) works with both settings.

There is some sort of hierarchy at work so that margins for individual cells can be changed. However, it would be great to have a clear explanation of all of this. 

As is often the case, Microsoft could help by making these distinctions clearer in the settings themselves. Alas, it rarely does that so we are forced to spend hours trying to figure this out. 

Anyway, you always have good insights and I look forward to your response.

The settings you see at Table Tools | Layout | Alignment | Cell Margins are the settings for the entire table; these are the same that can be set at Table Properties | Table | Options (note that the dialog that you get when you click that button is labeled Table Options). Apparently, even with a specific cell selected, those measurements do not change to reflect any settings that are made for that specific cell at Table Properties | Cell | Options.

Yes, but now I am trying to understand the logic of the settings in the two locations. Should I post that as another question?

I know that in other cases, Word offers various ways to arrive at the same settings. However, in this case there are two settings called "Cell Margins" that are not the same settings. I am trying to understand how these two sets of settings interact with each other.

I am also curious if there are any other settings with the same property--settings with the same name but that behave differently depending on how they were arrived at.

Indeed, margins can be set for the entire table, but those settings can be overridden for specific cells. If you find such cells, then checking the box for "Same as the whole table" should override the specific settings.