Answer
You are South 3rd seat, favorable.
What’s your call?. The Law of Total Tricks suggests that when your side has ten trumps, it’s safe to bid to the four level. There’s also the general principle to bid more whenever you have a void. Another consideration is that usually partner (having opened a weak two bid) has little defense, and accordingly the opponents almost surely have a game and possibly a slam. So we think it’s especially clear to bid four spades.
Bonus from Val: Less experienced players sometimes pass in this sort of situation, thinking that they will support spades later, and hoping that the opponents will not bid a game. It is true that, sometimes, less experienced opponents fail to bid their games. However, there are strong indications that it’s best to bid high now: (1) The South hand is very promising for offense ; (2) South probably will not take even one trick on defense; and (3) passing will give the opponents room to explore for their best fit and perhaps even to explore for slam.
The full deal appears on the next page, together with the actual auction from our table.