speculate

to believe especially on uncertain or tentative grounds

Scientists supposed that large dinosaurs lived in swamps

talk over conjecturally, or review in an idle or casual way and with an element of doubt or without sufficient reason to reach a conclusion

We were speculating whether the President had to resign after the scandal

reflect deeply on a subject

I mulled over the events of the afternoon

invest at a risk

I bought this house not because I want to live in it but to sell it later at a good price, so I am speculating