Verb tenses
The verb tense indicates time and duration of the verb:
Source
"Table of English Tenses." English Grammar On-line 4U. 28 Jan.2010. 31 Mar. 2010
http://www.ego4u.com/en/cram-up/grammar/tenses.
For additional discussion of verb tenses:
"Verb Tenses." Grammerly.com. 2019. https://www.grammarly.com/blog/verb-tenses/
For a discussion of conditional tenses:
Decker, Rob. "First, Second, and Third Conditional." Guide to Writing. Capital Community College Foundation. n.d. Web. 20 Aug. 2013.
Link: http://grammar.ccc.commnet.edu/grammar/conditional2.htm
For a discussion of can vs. could:
“Can or Could.” Learn English. British Council. 2014. Web. 15 Jan. 2014.
Link: http://learnenglish.britishcouncil.org/en/english-grammar/verbs/modal-verbs/can-or-could
Soanes, Catherine. “Can or Could.” OxfordWordsBlog. Oxford University Press. 1 Jul. 2013. Web. 15 Jan. 2014.
Link: http://blog.oxforddictionaries.com/2013/07/can-or-could/