We can help ensure future shoppers complete their purchase.
We can help ensure future shoppers complete their purchases.
The new law mandates city bikers wear a helmet.
The new law mandates city bikers wear helmets.
I believe I was taught that the pluralization of the subject must match the pluralization of the object. So, "mandates city bikers wear a helmet" would be incorrect, since it would technically imply those bikers were collectively wearing a single helmet. If we really wanted to use "a helmet", we could say "The new law mandates every city biker wear a helmet", since every singularizes biker.
But, common usage would imply both are correct. What's the proper form here?