I thought a spider is/was an insect

New2grammar

As you can see an expert has just disagreed with me

Hi New2Grammar,

I hope I am not that person you are referring to as expert. Before I get in further trouble with the real

experts, I will make this brief comment. Event the experts can be wrong for a long time before realizing

what believed to be the true or correct answer was actually incorrect. Well, scientists thought Pluto was

a planet. Now what do you make of that?

I thought a spider is/was an insect, but it is in fact an arachnid.

Use "was".  This is not reported speech!  (And the first part is not a universal truth anyway; it's a universal falsehood!)  This is one of the most typical patterns in the English language:  I thought it was ..., but (actually) it is ...

In the sentence in blue, "is" is completely and totally impossible in normal idiomatic speech -- except:

I thought (to myself) [pause] "A spider is an insect". 

Compare.  The first sentence below has indirect speech, but the others don't. The last sentence has a main clause in the present, thus allowing either tense in the subordinate clause.

My professor said that spiders are (were also possible) insects!  I didn't think they were (are not possible).  I think he is (was also possible) wrong.

CJ 

Firstly, I didn't notice that it was (can only use "was", "is" not possible?) not reported speech!  And universal falsehood.  What a phrase!  This is important because we are not talking about something that is always true.  As a result, we can only use the past tense in sentences starting with "I thought it was".  The "was" is not the result of backshifting.  It is used instead to indicate that the believe was hold true in the past but is now found to be false.

Secondly, both present tense and past tense are possible in reported speech when talking about universal truths or things that still hold true at the present moment.  This has been confusing me for a long time because I was taught to use the simple present in such cases and I thought *only* simple present is correct.  It has been troubling me because sometimes I saw past tense being used and I always wondered why.

While I was waiting eagerly for your reply, I opened Randolph Quirk's A Comprehensive Grammar of the English Language, which I recently bought from Amazon.  It doesn't mention the first point (or I just couldn't find it), but on the second point, it totally agrees with you!

You are really a great teacher!

Now, one last question.  Please forgive my insatiable desire to get to every details.  While both present tense and past tense are acceptable for the sample sentences you used, which of them sounds more natural?  Are the ones inside the brackets less natural / common?

EDIT:  I didn't see Barbara's post when I replied.  Thank you very much Barbara.  It's obvious that you also didn't see Jim's post when you replied.  I am so glad to also get the confirmation from you. Once again, I can take your answer to the bank!  I also want to thank Goodman, N2G and Marius for all your insights you have given me!

I always have problems on this.  How to avoid this confusion?

When I say "I thought", does it mean what "I thought" has to be false? 

 One small thing to add. The reported speech idea was brought into this thread by me and it confused everyone here. My bad. But when I included the thread for reference, I didn't suggest this topic was reported speech. I just wanted to point out that general truths can be said in the past tense. And that's why I said, it was be less related when I made the point. Sorry if you were confused by my statement.

I don't know, to me"I thought" comes very natural because I use it every day :) Lucky me

(Edit: actually, the reason it comes naturally to me is that when I say I thought I pictured a point in the past and
whatever I'm going to say next has to be in the past tense because it is a thought in the past, may or may not be real now! if you use the
present tense, it contradicts with I thought!!! It should be "I think" (what you're currently thinking )

I hope you understand my poor explanation. I've tried my best.
Another example,
I was so drunk, I thought my father was a women for a moment. (of course my father isn't a woman)
)