denken

to think [with an (+ accusative) ‘about something’ or accusative ‘something, e.g. a thought’]

"Ich denke, also bin ich."

not to forget; to remember [with an (+ accusative) ‘something to be brought along, etc.’]

"Denk an den Schlüssel!"

to imagine

"Das kann ich mir denken."

to think, to believe, to assume, to conjecture

"Ja, das dachte ich mir."