(to make) a conclusion, opinion, based on incomplete evidence

speculation, assumption

to form an opinion, give an answer, make a statement about (something) that is not based on very careful thought, calculation or definite knowledge

belief, speculation

(an instance of) speculating; (a business deal as a result of) speculating

theory, guess

the act of supposing something to be true but without proof; a guess

guess, belief

to guess (the usual word)

guess, conclusion

(an explanation of) the general principles of an art or science; a reasoned account offered to explain facts or events; an opinion or idea that is not necessary based on known facts or reasoning

hypothesis, belief

state of being uncertain; something which is uncertain

doubt, changeableness