为什么菲律宾宪法要规定总统候选人必须具有读写能力？难道还需要在宪法上避免文盲当总统吗？

菲律宾宪法第七条第二款规定：

任何人都不得当选总统，除非他出生时即为菲律宾公民，是注册选民，有读写能力，在选举之日至少年满四十岁，并且在选举前至少有十年是菲律宾居民。

No person may be elected President unless he is a natural-born citizen of the Philippines, a registered voter, able to read and write, at least forty years of age on the day of the election, and a resident of the Philippines for at least ten years immediately preceding such election.

为什么要明确规定要有读写能力？难道文盲还可能做总统吗？