Eben, i didn't miss that - perhaps i misinterpreted though. The decision to use the words "penalties...shall be paid upon notice...and assessed and collected in the same manner as taxes" is different in my opinion to saying "are taxes", in the same way as me saying "steak shall be eaten with a knife and fork in the same manner as pork" does not make a cow identical to a chicken. Moreover, the second half of the phrase "Except as otherwise provided, any reference in this title to “tax” imposed by this title shall be deemed also to refer to the penalties and liabilities provided by this subchapter." does nothing to suggest that the two concepts are necessarily identical in their legal usage outside of the IRC (such as the Constitution), or even within this particular subchapter (which would constitute the "as otherwise provided" exception) - rather, merely that they should be functionally treated as such when interpreting and applying other sections of the IRC. The reason i focused on the other sections were that they addressed how the penalties were intended to function in relation to other taxes in the code, and i thought it may be possible to distill from those functions some distinction between how, when and why the two classes of liabilities were imposed (which it turned out the answer was no). Of course, even if it had, that doesn't necessarily provide us with any direction as to how a court may choose to interpret the constitutionality of a particular liability - as is clearly demonstrated by Taft's opinion - however it may help to identify how and why the word is interpreted and used by different branches of government.