In a reply to a question about the sorites paradox, Professor Maitzen writes:
"Logic requires there to be a sharp cutoff in between those clear cases -- a line that separates having enough leaves to be a head of lettuce from having too few leaves to be a head of lettuce. Or else there couldn't possibly be heads of lettuce."
However, there is no justification that clearly leads from his premise to his conclusion: obviously we can have heaps of sand without knowing exactly how many grains of sand are required to distinguish a "heap" from a pile of individual sand grains, or else there would not be a so-called "paradox" in the first place!
The premise as he presents it sounds like a tautology, not a logical argument. What makes a "heap" of sand is not only how many grains of sand there are, but also how those grains are arranged. If you took a "heap" of sand and stretched it out in a line, you would have the same number of grains, but it would no longer be a "heap." You could take a head of lettuce and separate it into its individual leaves, but then you'd no longer have a head of lettuce. So you can clearly have a head of lettuce without knowing the exact number of leaves required, since we can easily validate that assertion through an appeal to empirical experience.
The sorites paradox tries to impose a degree of precision on a concept that by design is meant to be indeterminate in number. His answer does not address that consideration at all, but merely insists that a heap "must be" determinate in number or else it could not exist.