Topic: Mixing past and present tenses

[Franzilla]

Tell me, if I'm writing in past tense but I'm referring to something that is still the case today, is it okay to use present or should it all be in past tense? For example, which of these is correct?

Dad kicked his fins and glided on towards the shore. I’d read in my scuba instruction manual that sound travels farther underwater but my Dad’s ears defied that particular law of physics.
<doesn't this one imply that his ears are no longer immune to that law of physics? So should 'travels' also be in past tense?>

or

Dad kicked his fins and glided on towards the shore. I’d read in my scuba instruction manual that sound travels farther underwater but my Dad’s ears defy that particular law of physics.
<Here, only the dad kicking his fins is in the past, the rest – sound traveling farther and her Dad's ears - is in the present as it's still true???>

or

Dad kicked his fins and glided on towards the shore. I’d read in my scuba instruction manual that sound traveled farther underwater but my Dad’s ears defied that particular law of physics.
<does this imply that the physics law and her dad's ears are somehow not the same now?>

It's been a long day and I just can't get my head around this! Thank you!

[Anne Marie]

It is fine to mix them.  You have to have a sense of when the story is being told in relation to the events of the story, and then make it accurate grammatically based on that.

[AdamV]

I'd say "travels" because that part of the sentence is definitely on-going. Defy/defied could go either way, depending if Dad is dead, missing, has gotten hearing aids, etc. If nothing has changed with Dad, it would also be present tense. So, #2.

[MysteryRobin]

I believe that when writing in past tense, things that are *always* true are still written in present tense.

"I read that the earth revolves around the sun."
vs.
"I read that Jon lost the race."

[jancoates]

What about, "...dad's ears WERE defying..."? Doesn't this kind of detail drive you crazy?

[Franzilla]

Great. This makes sense, which is what I hoped. If it's not logical (ie everything has to be written in past tense just 'because I said so') then I'm unhappy. So I'm happy!