>

I mean this is just false. Things like pain are fundamental to life and evolved long enough ago to where it is a common ancestor. Also different species do not have radically different base neurology / nervous systems. Which is why we use lab rats / mice for studying drugs / neurology, because we can sacrifice them and things generally work the same.
Yes it is likely a spider can experience most things a human can, including nuanced emotions. Why do you suspect it can’t?
Especially capacity to suffer, it is one of the most fundamental things of life / evolution. Literally all life that has the capacity to avoid death / harm must have it.
Taxonomic classifications are built out around recognizable similarities in animals biological structures. Setting aside how precisely we understand brain function in non-human species, it takes little effort to see that most vertebrates are structured in a way that heavily overlaps with human biology. They are similar. Why would you assume they aren't?
And if you go from a "philosophical" perspective and ask how we could possibly know what they feel, you may well extend that to humans. How do I know you experience qualia?
You're getting so caught up in precision that you're overlooking obvious similarities. Can't see the forest through the trees. That animal has a nervous system and demonstrates a pain response. How much more detail do you need to be able to understand it feels pain?
For creatures without similar structures, we don't make the same assumptions about pain and suffering. Do carrots feel fear? Do mollusks weep? No one thinks about that. >

Except for the fact that many people claim to empathize with invertebrates or even plants. You clearly understand enough biology to think clearly about this topic. All I'm saying is that everyone else should make an attempt to meet that minimum standard of understanding. >


many people claim to empathize with invertebrates or even plants.

Very few claim to empathize with invertebrates, but crabs and lobsters and other crustaceans have pain responses too, so it's still not an example on your side here. My point was that people see similarity in responses and behavior, and that's made possible by our very real similarities. That Doctor so-and-so knows the science of it all and Dennis your vegan high school classmate does not makes no difference. 
The science explains why we have similarities and why we see and feel similarities that allow us to empathize. But not knowing the science doesn't invalidate the emotional feeling—the right answer is right whether or not you show your work.
As for people who "empathize" with plants, they fall into two categories: [1] People who are personifying plants because it's a useful rhetorical technique, but don't actually believe plants feel complex emotions; and [2] extreme outliers that don't merit serious consideration. If "crazy people believe crazy things" is your best defense here, you've lost focus on the "philosophical" question your post is about. >

We might just have different experiences when it comes to people's claims about the range of their empathy. I know plenty of not-crazy individuals who either claim to or speak as though they understand the feelings of an invertebrate. I might have a sampling bias because I spend a lot of time around animals and teach HS biology. 
I agree that the right answer is right whether or not you show your work, but showing your work is necessary to distinguish between the right answer and an answer that seems right, but isn't. It certainly seems like it'd be painful to be a clam being eaten by an octopus. This might even illicit a little bit of sadness for the clam... But upon further reflection I might realize that clams don't have centralized nervous systems. They don't have families that will mourn their demise. They don't have unfulfilled dreams or projects. I've now shown my work and realized that my previous answer was incorrect. >

Again, you're pushing out to extremes to justify your position, but if you have to run all the way to mollusks, animals without a central nervous system, to stick to your view, it sure seems like you've abandoned it for every animal that does have one.
And for those, there's no need for people to show their work. Because they're right. Someone else can check it for them. Verified. Instinct to empathy validated. >

Not necessarily. I used mollusks because it's a simple and easy case. I can make my point without getting lost in the details. We can ask the same question for animals of increasing complexity. You begin at simple cases, then move on to more difficult cases. >

When an animal or insect is trying to escape the stimulus, that's an indication that it's at best, 'bad' and at worst 'very painful.' It's quite easy to see when what you're doing causes an animal pain.
And as far as having empathy for a spider: maybe having a leg ripped off hurts, maybe it doesn't (see my last point below), but either way it's no longer at full-capacity, which is a situation that a person can empathize with: it's not unreasonable.
You say not to over-estimate pain receptors, but if the pain level is unknown, what about under-estimating them?
You also say it's complex and not-understood, but then you say to follow your understanding of it. If it's not understood, why is your understanding correct? >

Why does an attempted escape necessarily indicate pain? Even microscopic organisms move away from stimuli that aren't conducive to their existence. 
You can't empathize with a spider being at half-capacity because the human experience of a handicap is fundamentally different from the arachnid experience (if arachnids experience anything at all). At best you'd imagine a life where it's slightly more difficult to acquire food (minus the anxiety and hunger pains and social stigma and the plethora of other uniquely human experiences that cloud our judgement when empathy enters the picture). >

You say not to over-estimate pain receptors and consciousness, but if pain levels and the nature of consciousness is unknown, what about under-estimating them? And why do you think your correct about things that you say are unknown?

At best you'd imagine a life where it's slightly more difficult to acquire food

That's what I mean; at minimum, there's this to empathize with; it's not nothing >

I don't think that consciousness or pain is "unknown". You're conscious. You feel pain. You can empirically study these phenomena. We're far more likely to overestimate pain levels in non-human animals because humans are subject to greater levels of pain in a wider variety of "flavors." Underestimating the pain of non-human animals is certainly a danger (ask Descartes), but I think it's a less common one because of how complex our nervous system is. 
To be clear: I said that you ought to drop your pretense of knowledge, not that the topics are intrinsically mysterious. It's helpful to begin with a blank slate when studying complex topics because outside assumptions can make proper learning difficult. 
But that experience, the experience of having trouble finding food, is intrinsically linked to our humanity. Spiders don't have mammalian stomachs that rumble. They don't have the same receptors that send hunger pangs. They don't have salivary glands that cause their mouth to water when they think of food. They don't have hands that get shaky when they're malnourished. When you strip the experience of all the anthropological features, you're left with nothing. >


humans are subject to greater levels of pain in a wider variety of "flavors."

Can you explain this, please? I think I disagree, but I want to know what you mean first.

Underestimating the pain of non-human animals is certainly a danger (ask Descartes), but I think it's a less common one because of how complex our nervous system is.

Therefore, empathy is not a poor tool when thinking about animal suffering?

I said that you ought to drop your pretense of knowledge, not that the topics are intrinsically mysterious. 

If there aren't concrete answers and measures, there is mystery. If this wasn't somewhat vague / mysterious, we wouldn't need this CMV

When you strip the experience of all the anthropological features, you're left with nothing.

You talk about the complexity of nervous systems, but then have this very reductionist conclusion here about being 'left with nothing'? >

Humans experience greater levels of pain when responding to similar stimuli. Our sensory organs (especially our pain receptors) are very finely tuned compared to most other species (obviously there are exceptions like the eyes of hawks, the noses of dogs, and the ears of bats, but generally this holds true). In addition to this, humans experience social and psychological pains. We experience rejection, depression, anxiety, shame, and a whole slew of other negative emotions. Other animals (especially social ones) experience some of these emotions, but humans do something uniquely masochistic: we dwell on these pains. We have minds that can become torturous as they replay the most painful moments of our lives. 
I don't think that empathy has anything to do with general estimates of the capacity for pain of non-human animals. 
Concrete metrics aren't necessary for a mystery to be dissolved. You can have clarity about a topic without rigorous measurements. This is why we have things like literature, poetry, music, and philosophy. 
Yes. Exactly. The complexity of the nervous system is precisely what gives rise to the layers of an experience. If I move from one nervous system to another totally different one, I lose those layers. >


Humans experience greater levels of pain when responding to similar stimuli

This sounds… questionable. What’s your source for this?
From my admittedly limited understanding of psychology, this doesn’t even sound measurable. You can only measure pain via response to pain (i.e. behaviour), or via cognitive imagery like EEGs.
Neither of these allow for comparison with animals. Animals can exhibit very different behaviours from humans despite the same stimulus (more basic example: dogs pant instead of sweating, doesn’t mean they feel less heat), and brain imagery is obviously only applicable to humans. >


An octopus? A crow?

These are two of the smartest animals in the animal kingdom >

True. But intelligence and capacity to suffer aren't the same thing. >

perhaps, but it seems to fairly correlated to consciousness. >

I think that you're probably right. If I were to make a bet, I'd probably gamble that corvids, apes, cetaceans, and cephalopods probably experience the most pain. >

Your view is just a fact. Of course I cannot experience the same neurological process as a spider. To counter argue this is so absurd to even propose that anyone holds this view constitutes a straw man.
Your view is easily dismantled when you switch out empathy for sympathy.
Understanding that getting stepped on and crushed to death sucks is something that anyone can understand and doesn't require a spider brain. >

I disagree. Why does getting stepped on suck? Well, because it would hurt. Why would it hurt? Because I have a nervous system with a certain structure that responds in certain ways to certain stimuli.
Now, how can I know that being stepped on sucks for spiders? I'd have to study the nervous system of a spider to see if there is sufficient similarity to justify my judgement that "That'd suck." 
Frankly, I don't even know if a spider experiences anything at all. But that's probably too long of a conversation to have here. >

Why does getting stepped on suck? Well, because it would hurt.
Because it would kill. That spider is no longer alive. 
Most people agree that dying sucks. >

Most people, sure. Some people really want to die. Most animals probably want to continue living. As we move from more complex to less complex species, it's unclear where organisms stop having things like desires. Do dogs want to continue living? Probably. Birds? I think so. Lobsters? Uhhhh...I don't know. I'd put it at 50/50. Spiders? Probably the same as lobsters. Clams? Probably not. Sponges? Almost certainly not. 
Most people agree that dying sucks. I'm unsure what most spiders think. One thing is certain: sponges do not think that dying sucks. They don't think at all. >

Ok, but we're talking about people's empathy towards animals, Not necessarily what the animals think. 
It's about what the people think, 
If a person is getting abused by their wife, And this guy is fine being treated badly, and doesn't want to leave her, does that mean that the people That feel bad for him are wrong?
Even if the animal doesn't want to continue living, The people know they want to continue living, So if they see something else die that makes them think about themselves dying. >

In that case, empathy might serve as a reminder of one's mortality, but it's not really doing anything to help the empathizer learn anything interesting or helpful about the dying animal. >


Most people's opinions about animal rights and animal suffering are informed by a gut feeling of indignation/guilt/sadness when they see an animal responding to a negative stimulus.

Sure I guess I agree with this. I'd say it goes beyond pain though. 

Here's the issue: pain is a really complex set of processes that are intrinsically linked to the structure of an organism's nervous system.

Agreed

Feeling empathy for an abused dog only makes sense insofar as the dog has neurological structural similarities to you. 

Disagree. While that helps, humans like to map our own experiences onto other organisms regardless of how similar they are to us neurologically. 

The further away we get on the evolutionary tree, the less empathy makes sense. Empathy for a spider? An octopus? A crow?

Again disagree. People don't take evolutionary closeness into account in any context. Organisms that may be distantly related to us could have evolved similar attributes via convergent evolution. This is completely irrelevant. 

Uf you claim to care about animals you should drop any pretense to understand what they're feeling and get a basic understanding of the variety of nervous systems in the animal kingdom and how those systems respond to stimuli.

You seem to disagree with yourself here. One, with lots of animals we have a pretty good understanding of their behavior when in distress, take any lab animal as an example of this. Second, many animals will exhibit traits similar to humans when in distress. Now I'll agree that it's important to not misinterpret an animals responses but some are quite unmistakable and we do research into animal behavior as well. 
It seems to me you're proposing we stop using empathy so we can research how animals react and experience distress then, once we know, go back to using empathy. >

I don't see how you disagree with points 3 and 4. You're making claims about what humans like to do and what humans actually do. I'm making claims about what humans have rational justification for doing. I'm saying that it's nonsensical to attempt to empathize with a spider. I know that some people will disregard the structural dissimilarities, and that's the problem. >

I'm saying, why? Why can't we empathize with it? Is your requirement that we understand how spiders exhibit stress, discomfort or distress? If so, and if someone knows those expressions and a spider is expressing them why is empathizing with it bad? Why is it bad to empathize when a bug misses a meal? Or when it loses a leg? Certainly it isn't experiencing those things as a human would but I see no reason why we can't empathize with them. >

Then you're not empathizing, you're just having a strange fantasy about the inner life of bugs. >

What? No, you're empathizing with a creature in distress. >

If you're experiencing something and I claim to be empathizing with you, but I completely mischaracterize the experience you're actually having, am I actually empathizing? >

Using your own argument and other comments you’ve made, there is no way to truly know how anyone feels at any given moment. Let’s just throw all empathy out, no? Forget the spiders, who cares for them, right? Let’s talk about humans. If we can’t prove a human is in distress scientifically, why feel empathy for them? We can see their response to stressful stimuli, but how do I know your response is the same as mine? If could tickle you if you placed your hand on a fire. Or let’s say they are exhibiting signs or distress, like a spider or other creature far from us on the evolutionary grid. People are also more complex, they can lie. Some can even alter their emotions, look at actors, look at psychopaths.
Why use empathy in any capacity at all? You’re not in another persons body or mind, you’re not in a dogs body or mind, you’re not in a spiders body or mind. >

While I think that this argument is philosophically sound, I don't like solipsistic arguments. They lead to a paralysis of the mind. >

Empathy may not be perfect, but it's the best tool we have.  Experience and experiment shows it works well for mammals and birds.   They experience pain and emotional distress in a very similar way to us. >

How could you possibly know that? Is your grandmother a raven? >

Not my grandmother, but if you go back far enough, we have a common ancestor. >

All I learned from this is that the swedes are heartless beings >

Perhaps you learned they have a heart even for inanimate objects. >

its not a poor tool, simply not one that can be applied to every animal,  and people who like dogs can still murder spiders without a shred of remorse, so its also not one used on every animal or required to do so. >

It's a tool that rapidly loses efficacy as you move further away on the evolutionary tree. It's a decent tool for other humans. It's probably sufficient when it comes to non-human mammals. It's absolutely useless when it comes to invertebrates. >

I'd say it's a fine tool to use given we can't actually experience life like them. >

That's precisely why it's a poor tool. Your empathetic response will always be closed by anthropocentric sentiments. Rather than trying to "put yourself in their shoes," you might consider taking their shoes and performing every sort of scientific/empirical test on them to see if you can understand a little more about the situation. >

Would it not be safer to assume they experience pain? So as not to go around torturing creatures needlessly because we simply can’t prove they experience pain the same way? Would you rather not use empathy and an unknowingly inflict terrible pain on invertebrates? Or rather use empathy and kill them humanely to avoid the possibility you’re causing undue harm? 
Using empathy actually works against your own argument, the unknown. We can’t prove they don’t experience pain the same way, we can’t prove they do either. Wouldn’t it be a better measure to assume they do? Squash them quick and fast (if you must kill a spider, I let them live) instead of setting them on fire or ripping it’s legs off so it dies from lack nutrition. >

I think that your reasoning here is great. I think that we ought to err on the side of caution when it comes to animal suffering (both human and non-human). I don't think that empathy is required to make this argument. I think that it just gets in the way. >

If a dog is yelping or whimpering, the meaning is pretty clear. >

Is it? Animals with complex nervous systems and social systems exhibit a wide variety of responses to a wide variety of stimuli. Additionally, many abused dogs are trained not to yelp or whimper. An intelligent dog might realize that whimpering and yelping is a good way to get their human's attention. The meaning is not always clear. >

The pragmatist philosopher G.H. Mead has an argument about the philosophy of psychology that's relevant here. In contradistinction to behaviorists, he argued that there were "universals" in behavior that the psychologist could study. These universals were not particular stimuli, nor even particular responses to stimuli, but what was characteristic about a range of stimuli that elicited a similarity of response across kinds of situation. 
If we're talking about pain, "pain" would have something characteristically universal about it in humans if it turned out that much the same kind of stimuli elicit pain across people. Fire, in this sense of universal, is universally painful. 
At the right level of generality—say, where a flinch becomes just a variety of withdrawing from a stimuli, amongst which there are other varieties—there are a range of stimuli (like fire) that elicit similarity of responses—in this case, responses that can all be glossed as "withdrawing"—across different animal kingdoms. 
Mead also makes the argument that when we recognize something as what it is—that is, for example, my dog as a dog—what we are doing is responding to those characteristics in it that are universal in other particulars that we would recognize as being of its kind (e.g., barking, four legs, etc.). Likewise, if we are able to understand pain as eliciting a similarity of response, we can recognize a response to any given painful stimuli as being recognizable because we understand what pain is. 
A parallel argument—by the phenomenologist Alfred Schutz—points out that this act of recognition is empathetic. His grounds for thinking so are that we understand what others are feeling, etc., by imagining ourselves in similar circumstances and thinking about how we would respond. It need not be possible for us to have actually undergone the experience ourselves, even (one reason why sentences like: "how would you feel if someone tore your legs off?" said to a kid doing that to a spider, often works to convince him that would be painful). 
Taking Schutz and Mead together, we can say that empathy is an effective tool for getting people to think of a variety of animal suffering as painful insofar that it's able to get them to recognize that, were they in a similar circumstance as the animal, they would feel pain. This argument would work insofar that recognizing behavior as "painful" does not depend on either self-sameness of stimuli or of responses but, rather, the ability to notice similarities between stimuli and responses that can be glossed as universally characteristic of that type of stimuli or response. >

I like the argument from Mead, but there's a massive problem with Schutz's characterization of empathy: A child having his legs ripped off would illicit a pain response. It's unclear whether arachnids can feel anything we can justifiably call pain. The empathy response ultimately fails to capture an accurate picture of reality because it ignores the neurological dissimilarities between the two organisms. 
The same exact thing can happen with humans. "How would you like to be slapped in the face and degraded?" This question hits differently for a masochist than for an abuse victim. >

Do you believe animals, at least the more intelligent ones, have a sense of self-awareness? >

Yes. I believe that most vertebrates have something that we could justifiably call self-awareness. >

This is just a thought experiment. There is no correct answer.
What do you think would be worse
Knowing that you are being torture or just experiencing pain? >

The psychological pain that comes from the helplessness of knowing that you're being tortured would mean that knowing that you're being tortured would be more painful than simply experiencing the pain from the torture........
Unless you're a really committed masochist. Then you might feel a counterbalancing pleasure that would make the pain more bearable... So I guess it depends on the psychological makeup of the individual. >

Let's keep the extremes away for the sake of the argument. Outliers exist no argument.
Now, as a person being tortured would probably suck right? >

In almost every case torture would be one of the worst things a human could endure (I think by definition). Sounds awful. >

Yeah, hope I never go through it. 
If someone you knew was tortured, maybe a woman kidnapped or a soldier captured. You'd be able to imagine that would suck, you wouldn't be able to relate but you could understand the stuff that they went through was horrible. Yeah? >

If an average woman I knew were tortured I could relate to certain aspects of the situation. I know what pain feels like. I've felt fear. I've felt hopeless. I wouldn't be able to relate to every aspect of the situation, but I could probably jigsaw together a basic picture of her mental state at the time. At the very least, I'd be able to understand that they've gone through something traumatic and horrible and altogether suboptimal, yes.