What Is Probably True
Modal Verbs of Probability - Present
Modal verbs of probability express an opinion based on what a speaker knows about a situation at the moment of speaking. The following forms are used to speak about present situations.
Example:
Bob might be able to find a job in silicon valley.
I must be trained to use the shell effectively.
Josh might be able to salvage the kernel.
Present Forms
'Must' plus the verb expresses the idea that you are almost 100% sure of your opinion about a given situation.
Subject + must + base form of verb + objects
Example:
I must be trained to use the shell effectively.
They must be looking for a shortcut.
Use 'might' or 'could' to express an opinion that you think has a good possibility of being true.
Subject + might / could + base form of verb + objects
Example:
Josh might be able to salvage the kernel.
Jane Fonda might be willing to market our killer app.
'Can't' plus the verb expresses the idea that you are almost 100% sure that something is not true.
Subject + can't + base form of verb + objects
Example:
The boss can't be serious about using a sniffer program to monitor internet use on site.
A laptop can't be replaced by an iPod or iPad.