[jhedwards]

They left out the second half of the sentence: 非 [not] 常 [eternal] 道 [way]

Classical Chinese is highly contextual, and characters take on different meanings depending on the position in the sentence and the narrative context, hence the second instance of 道 meaning "speak, expound" instead of "way, method".

My favorite instance of this is from the Zhuangzi: 物 [thing] 物 [thing] 而 [and/under those conditions] 不 [not] 物 [thing] 于 [among] 物 [things]

Which translates to "treat the things of the world as things, but don't be a thing among them" which means that you should use strategic thinking to avoid becoming a victim of circumstances.