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It is not that 'could' IS the Past Tense of 'can', but that one of its USES is as the past tense of 'can'.
'took' is the Past Tense of 'to take' - and that's all it is. It has no other uses or function. ‘hit’ is both the Present Tense verb, and the Past Tense of ‘to hit’.
The modal auxiliary verbs each have a number of different uses. If you look up 'could' in the Oxford dictionary, you will see it gives six different uses; and grammar sites will list even more!
Your sentences are polite requests, and any request is asking someone to perform an action. Since the action can only come after the request, then all requests are for a ‘future action’.
As I say – if you see any past tense use of a modal as just ONE of its uses, then you will be less mystified. 
Bazza
It is not that 'could' IS the Past Tense of 'can', but that one of its USES is as the past tense of 'can'.
'took' is the Past Tense of 'to take' - and that's all it is. It has no other uses or function. ‘hit’ is both the Present Tense verb, and the Past Tense of ‘to hit’.
The modal auxiliary verbs each have a number of different uses. If you look up 'could' in the Oxford dictionary, you will see it gives six different uses; and grammar sites will list even more!
Your sentences are polite requests, and any request is asking someone to perform an action. Since the action can only come after the request, then all requests are for a ‘future action’.
As I say – if you see any past tense use of a modal as just ONE of its uses, then you will be less mystified.
'took' is the Past Tense of 'to take' - and that's all it is. It has no other uses or function. ‘hit’ is both the Present Tense verb, and the Past Tense of ‘to hit’.
The modal auxiliary verbs each have a number of different uses. If you look up 'could' in the Oxford dictionary, you will see it gives six different uses; and grammar sites will list even more!
Your sentences are polite requests, and any request is asking someone to perform an action. Since the action can only come after the request, then all requests are for a ‘future action’.
As I say – if you see any past tense use of a modal as just ONE of its uses, then you will be less mystified.
Okay, first, thanks for response.
I found the word "Could" on the Oxford Dictionary as you mentioned. It says that Could is a "Past of Can". So basically it's a past tense of Can.
I also searched for it's grammar functionality, which i found that a word "Could" can be used for Past, Present, and Future. This is MORE confusing to me.
Why? It's because Could is a Past Tense of CAN. However, Why can a Past Tense word CAN be applied to situation to talk about Present AND Futre.
If there is no logical rules on usage of proper timing, then why can't i use a future word of "Will" for Past situation?
Once again, thanks in advance to whom may respose to my questions.
Bazza
Think of the verb ‘to have’: to own, to possess.
“He has a Honda, and I have a Mazda.”
Yet here it is, being used as an auxiliary verb to form the Present Perfect, Past Perfect, and Future Perfect:
“I have had my car for five years.”
“I bought a new car because I had had my old car for five years.”
“In a few months, I will have worked here for ten years.”
Think of the verbs ‘to hit’ and ‘to read’. Both are MAIN verbs, yet:
‘hit’ and ‘read’ are the Present Tense, Past Tense, the Present Perfect and Past Perfect, and Future Perfect:
“Now, hit the ball with the cricket bat and run!”
“Yesterday, he hit the ball so hard it went out of the field."
“..have hit…”
“…had hit…”
“I will have hit…”
Some MAIN verbs , like ‘drove’, only occur in the Past Tense:
“I DRIVE to work each day.”
“Yesterday, I DROVE to work.”
“I have DRIVEN to work every day this week.”
“I will DRIVE…
“I will have DRIVEN…”
ALL the modals are AUXILIARY, ‘helper’ verbs, not MAIN verbs. They are used in the tenses and Conditionals and hypothetical statements TOGETHER with a MAIN verb.
‘can’ refers to present possibility: “I can play the piano.” We use ‘could’ to talk about possibility in the Past and Future:
“Before I had my accident, I could run a mile in under eight minutes.”
“My coach says that, if I train hard, I could be a top athlete one day.”
I want to stress to you that ‘could’ is not a MAIN verb and not that it IS the Past Tense of ‘can’, but that ‘could’ is an auxiliary verb USED to form the tenses. None of the modals occur on their own – they are always combined with a MAIN verb.
“He has a Honda, and I have a Mazda.”
Yet here it is, being used as an auxiliary verb to form the Present Perfect, Past Perfect, and Future Perfect:
“I have had my car for five years.”
“I bought a new car because I had had my old car for five years.”
“In a few months, I will have worked here for ten years.”
Think of the verbs ‘to hit’ and ‘to read’. Both are MAIN verbs, yet:
‘hit’ and ‘read’ are the Present Tense, Past Tense, the Present Perfect and Past Perfect, and Future Perfect:
“Now, hit the ball with the cricket bat and run!”
“Yesterday, he hit the ball so hard it went out of the field."
“..have hit…”
“…had hit…”
“I will have hit…”
Some MAIN verbs , like ‘drove’, only occur in the Past Tense:
“I DRIVE to work each day.”
“Yesterday, I DROVE to work.”
“I have DRIVEN to work every day this week.”
“I will DRIVE…
“I will have DRIVEN…”
ALL the modals are AUXILIARY, ‘helper’ verbs, not MAIN verbs. They are used in the tenses and Conditionals and hypothetical statements TOGETHER with a MAIN verb.
‘can’ refers to present possibility: “I can play the piano.” We use ‘could’ to talk about possibility in the Past and Future:
“Before I had my accident, I could run a mile in under eight minutes.”
“My coach says that, if I train hard, I could be a top athlete one day.”
I want to stress to you that ‘could’ is not a MAIN verb and not that it IS the Past Tense of ‘can’, but that ‘could’ is an auxiliary verb USED to form the tenses. None of the modals occur on their own – they are always combined with a MAIN verb.
Thanks for response. I think it helped me understand better regarding Helping verbs.
Your sentence of "“My coach says that, if I train hard, I could be a top athlete one day.” If i put, "“My coach says that, if I train hard, I WILL be a top athlete one day.” Is that the same meaning? Isn't it more appropriate to use WILL because of future empahsis?
Thanks Bazza
