regex question

I am writing some regex on a php form to validate input and have come up with this, for example - if (empty($first) || !eregi("^[A-Za-z]+[- ]?[A-Za-z]+$", $first)) for checking a persons name. This allows a single name, or a hyphenated double name, or a non-hyphenated double name, and it works. My question is this - why is the third set followed by a '+' optional? I thought the + meant the preceding group is present 1 or more times. The ? means the preceding group is present 0 or more times. Why is it that when I put a ? in the place of the + after the last ] if (empty($first) || !eregi("^[A-Za-z]+[- ]?[A-Za-z]?$", $first)) the regex is broken? Regards, Chip