I have claimed more than once that, necessarily, to think is to think of something. But is that right? Perhaps one can think something without thinking of something. That would be a spanner in the works.
Suppose I think that Tom is tired. The parsing could be done like this: I/think/that Tom is tired. This suggests that one can think without thinking of or about anything. One thinks something (e.g., that Tom is tired) without thinking of something.
It is clear that to think that Tom is tired is not to think of or about the proposition that Tom is tired, although of course one can think about that proposition, as when one thinks, of that proposition, that it is true or that it is a proposition. But I cannot think that Tom is tired without thinking about Tom. Nor can I think that Peter is taller than Paul without thinking about both Peter and Paul. If I am thinking that nothing is in the drawer, or nobody is at home, then I am thinking about the drawer and the home, respectively. If I am thinking that the null set is unique, then I am thinking about the null set. If I am thinking that wisdom is a virtue exemplified by few leftists, then I am thinking about wisdom and about leftists.
So it looks like I saw a ghost. I was scared there for a minute. Necessarily, to think is to think of something, if not directly, then indirectly as in the cases cited.