If you consider someone to be attractive...
If somebody reminds you of another person...
If an idea occurs to you...
If you suspect something is true...
If you recollect an experience...
If you memorize a number...
If you analyse a problem...
If you doubt something that you've heard...
If you can't comprehend something...
If you contemplate your future...
it comes to your mind suddenly.
you learn it so that you won't forget it.
that is your opinion
you think about it for quite a long time
you think it probably isn't true
they make you think of that another person.
you don't understand it.
you think about it in a logical way.
you think about it at a later date
you think it might be true but you aren't sure