I think I will have a pizza for dinner.
I think you are an idiot.
I think about you a lot.
I think there are some very strange people in the world.
Then you have:
I'm thinking about getting a tattoo.
I'm thinking of you (sympathy).
In none of the examples I have come up with, can you follow "I think" or "I'm thinking" with "to" or an infinitive.
Usually when we want to follow "think/thinking" with a verb, we use:
I'm thinking of getting my legs waxed.
I'm thinking about buying a new car.
I think I have flu.
I think I'll go to sleep now.
As you can see, none of these involve the infinitive or bare infinitive.
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