People here are confusing “digits” with “numbers.” Numbers are those things that have quantity, regardless of which base is being used. Digits are the representations we use to express numbers.
In our base 10 system, we have, not surprisingly, ten digits we use (maybe it is surprisingly, since the Romans had the same system, but used a wholly different set of “digits”): 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
The names for these are zero, one, two, three, four, five, six, seven, eight, nine. Not shockingly, they correspond to their numerical counterparts. That is, the name for the digit is the name we use for the number it represents.
“Ten” is not a digit. It’s a number. It is ((((((((1 + 1) + 1) + 1) + 1) + 1) + 1 ) + 1) + 1) + 1 of a thing. We represent it in our system with the digits “one zero”, written 10. We then say “ten” for that representation.
When you are in base eight, 10 no longer represents “ten.” Ten, you will recall, is a number. 10[sub]8[/sub] represents “eight.” 11[sub]8[/sub] represents “nine.” 12[sub]8[/sub] represents “ten.” If you say “ten base 8” you are meaning 12[sub]8[/sub]. You cannot possibly mean 10[sub]8[/sub], because that representation is not the same as the number 10.