to make up the day only.

The intention for every obligatory fast must be set during the night and must designate the specific day, though it is unnecessary to articulate that the fast is obligatory. A voluntary fast, by contrast, is valid even when the intention is formed in the daytime, whether before or after the sun’s zenith. If someone says, “If tomorrow is a day of Ramadan, then my fast is obligatory,” this conditional intention does not suffice, and whoever resolves to break the fast has in fact broken it.