Can I say this and is there a rule?
When we use "could/would have pp" to refer to future possibility, sometimes lack of if-clause will make the sentence ungrammatical (e.g By the end of this year I could/would have saved some money.)
But at some other time it is OK to dispense with the if-clause.
(e.g. "...the original cost of the dam was estimated at $25 billion, but by the time it is completed this could have risen to $75 billion or more.")
I don't know why it is the case. Is it because the dam example imply a condition?
So can I think for "could/would have pp" to refer to future possibility, an condition is necessary for them to work, be it implied or stated?
And can I say "...the original cost of the dam was estimated at $25 billion, but by the time it is completed this would have risen to $75 billion or more."?
Thank you.