Why is it not possible to have fog without dew?

Fog is when the cloud base is at ground level. Clouds form when the air temperature is at or below the Dew Point. The Dew Point is the temperature at which water vapour in the air condenses to form liquid water. read more

You can have dew without fog because there are ALWAYS trace amounts of moisture in the air, and when the temperature is cooler in the morning, the moisture condenses on the ground and you get dew. However, no matter what happens, if you have fog, you have moisture, and if you have moisture, you have dew. read more

The air around you contains moisture. But the colder the air, the less moisture it can contain. As the temperature right above the ground, and around you, drops to what is called the dew point temperature, or 100 percent relative humidity, it has to condense into droplets. read more