Rather than being too purist in our approach to tagging questions for the time period of relevance to them, I suggest a pragmatic guideline of using time period tags in this order of priority:

1. Named time periods
2. Century when 18th century or earlier
3. Decade when 19th century or later because by the 19th century governments begin to take a census every 10 years suggesting that too much changes in 10 years to assume that what was true 10 years earlier still holds.

Users will not need to know that decade tags prior to the 19th century should not be used if each decade tag in the 18th century and earlier is made a synonym of its century tag.

Rather than being too purist in our approach to tagging questions for the time period of relevance to them, I suggest a pragmatic guideline of using time period tags in this order of priority:

1. Named time periods when they are more or less recognized universally (at least in the English-speaking world) e.g. world-war-1, world-war-2, us-civil-war
2. Century when 18th century or earlier
3. Decade when 19th century or later because by the 19th century governments begin to take a census every 10 years suggesting that too much changes in 10 years to assume that what was true 10 years earlier still holds.

Users will not need to know that decade tags prior to the 19th century should not be used if each decade tag in the 18th century and earlier is made a synonym of its century tag.

Rather than being too purist in our approach to tagging questions for the time period of relevance to them, I suggest a pragmatic guideline of using time period tags in this order of priority:

1. Named time periods
2. Century when 18th century or earlier
3. Decade when 19th century or later

Rather than being too purist in our approach to tagging questions for the time period of relevance to them, I suggest a pragmatic guideline of using time period tags in this order of priority:

1. Named time periods
2. Century when 18th century or earlier
3. Decade when 19th century or later because by the 19th century governments begin to take a census every 10 years suggesting that too much changes in 10 years to assume that what was true 10 years earlier still holds.

Users will not need to know that decade tags prior to the 19th century should not be used if each decade tag in the 18th century and earlier is made a synonym of its century tag.