Can or Could, Shall or Should, Will or Would?

[Adobo]

This confuses me.  I can say “I can/will/shall do that” and “I could/would/should do that” and either way sounds correct. Where does the difference lie? And also does this have something to do if it’s use in past or present tense?

[LauraM]

This confuses me.  I can say “I can/will/shall do that” and “I could/would/should do that” and either way sounds correct. Where does the difference lie? And also does this have something to do if it’s use in past or present tense?

There are some differences between all of these words.  Some of those differences are subtle. 

"Can" is the present tense of the verb, meaning that you have the ability to do something. 

As in "I can talk to her."

"Could" is past tense of "can."  As in "Yesterday I could talk to her."

But "could" is also used to express doubt or uncertainty.  Meaning that you have the ability, but that you might or might not do something.  As in:  "I could talk to her but I'm reluctant to do so." 

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"Will" is the future tense of any verb.  As in "Tomorrow I will travel by train" or "I will read that book next week."

"Would" is the past tense of "will."  It is also a conditional, meaning it is used to express imagined consequences of an action.  As in "If I went outside today without my jacket I would get too cold."  Or "If I left my laptop unattended at the train station it would get stolen."

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"Shall" is future tense but is rarely used in American English; it has been replaced by "will"  to indicate future.  "Tomorrow I shall have a meeting with them."  But it's more typical to say "Tomorrow I will have a meeting with them."

But "shall" is still used in British English." 

"Shall" can also be an expression of politeness, as in "Shall I get you another cup of tea?"  You might occasionally used in American English in this manner.

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"Should" implies obligation.  "Today I should have a meeting with them."  It can also be used for future tense as in "Tomorrow I should have a meeting with them." 

Past tense is "should have."  As in "Yesterday I should have had a meeting with them."

[Adobo]

Thank you, Laura. See, sometimes I use those words without being aware if I’m using the proper one. You've explained it very well and here, I’m going to try to use them depending on what I learned from your instruction.

Will you look at this example if I used those words correctly? I could have done this yesterday but I wasn't online. I can do it now though. I will wait should there be any correction. Thanks.