# If the set of finite binary strings is enumerable, why isn't the set of infinite binary strings countable?

It can be shown that the set of binary strings is countable by enumerating the natural numbers through the combinatorial possibilities, using this pattern. Why can't the same argument be used to show that an infinite binary sequence is countable? The tree I have made along with the enumeration drawing corresponds to {},{0},{1},{0,0},{0,1},{1,0},{1,1}...

An answer I saw to a similar question here stated that this would only enumerate through the finite sets of binary strings but not the infinite sets, but I fail to see why this doesn't reach the "infinite" binary strings, since this sequence could go on forever.

• Where does the string of "0000..." which goes on infinitely long appear in your order? I think you're conflating "the set of infinite strings" with "the set of all finite strings." – Milo Brandt Oct 13 '19 at 2:19
• When you do a proof by induction, do you ever hit an "infinite" natural number? For the same reason, your construction will never consider an infinite binary string. – Nicholas Viggiano Oct 13 '19 at 2:58