past/present tense

Hi,

Let's say a car travels from A to B and it takes/took 30 minutes.

Either sounds accepable to me, although I prefer present tense. One consideration is the word 'it'. Does 'it' refer to the car or is it a non-specific 'it' (eg It takes 6 hours to fly from Toronto to Vancouver')? For the later, I'd definitely use present tense.

Firstt, place a card on the desk. Next, apply chemical Y to the surface of the card. Since you didn't/don't soak the card in chemical X before applying chemical Y, the card will catch fire.

'Don't' is clearly wrong here, I guess for the reason you have mentioned below.

I believe in both sentences above, past tense verbs are needed. Although grammar rules say that instructions/hypothetical situations can take present tense, it is necessary to use past tense when refering to past actions, for example, instructions before the current instruction.

So, your point is well taken, but I think  it's hard to generalize about all such situations.

Best wishes, Clive

Hi,

I don't understand why you said it is hard to generalize. Could you give me some examples where instructions can take present tense when they refer to previous instructions?

If I could have thought of a good example, I would have offered it to you. It's just that my intuition makes me feel that I don't want to generalize about this, although of course you are welcome to if you wish to. Language can be a very flexible thing. I'm not even 100% clear in my mind as to the terms we are using to discuss this case. I wouldn't exactly call Since you didn't/don't soak the card in chemical X before applying chemical Y a previous instruction. It's more like a simple comment.

Possibly you could say this kind of thing. First, place a card on the desk. Next, apply chemical Y to the surface of the card. Because the card is not soaked in chemical X, the card now catches fire.

Best wishes, Clive