Need help on "change of species" in sin

I need help understanding what it means for a sin to change species. For example: Someone has an impure thought of someone. Now what if this thought was brought on by listening to or remembering something said of a sexual nature. Does this “circumstance” change the species of the actual sin of “impure thought”?

To quote Hillary, “What difference at this point does it make!”

An impure thought, if entertained is a sin. I never heard of this change of species. :eek: Too many science fiction movies! :hypno:

:sad_yes:, it certainly is possible for the human being is be morphed into a demonic entity. All it takes is free-will + the abuse of freedom + hatred of God and his servants.

The process of morphing, which is started and fostered on planet Earth, is concluded at the time of judgment, where one enters either Heaven or Hell.

Hatred of God the ones who love him cause eternal damnation. How do you foster such an unnatural character? By purposely altering your mind to equal that of Satan. By listening to thoughts of sensuality and pride more than thoughts of the heavenly treasures, you gradually make yourself into a demon, a weed to be cut off and thrown into the fire.

A good rule of thumb: If you wish to enter Heaven, focus your thoughts on Heaven and think like an angel or a saint. If you desire Hell, focus your thoughts on evil and think like Lucifer did when he foolishly rebelled.

When one talks about species of sin, this is the sort of language used in very complex theological works, most notably the Summa Theologica of St. Thomas Aquinas. It is not really the everyday language of the Church and not something ordinary Catholics need get too worried about.

That said, St Thomas happens to directly answer your question:

“A circumstance never transfers an act from one species to another, save when there is another motive.”

Also note that sins of thought are not really a species of sin. The species, for example, would be say lust or adultery. Sins of thought are a type of sin, the others being sins of word and sins of deed.

You could read further, and probably only confuse yourself further (most people will, it is complex, wordy, and heavy stuff), here:

Thanks! What does he mean when he says “another motive”? So basically the sin of lustful thought would not be changed by these details

Another motive would be presumably referring to the intentions of the person; that the same ostensible act may be morally different depending on intentions and circumstances.


It is not sinful to look at nude pictures of people if one is studing for a medical degree.

It is sinful to look at nude pictures of people if one is wishing to seek some sexual enjoyment (in though or otherwise) from it.


It is not sinful - in fact good - to give to the poor out of charity.

It is sinful to give to the poor so other people will think better of you.

Not too sure really - maybe a Thomist could help clarify.

But in short, yes, any sin of lustful thoughts would seem to belong to the same general species (of lust, adultery, or whatever we might call it).

The circumstances that lead to the thoughs might change to culpability though, which is another matter.

No, that would not change the species. Let me explain.

First of all, what is meant by “species”? That is just a fancy term that means “what kind of thing something is.” For example, there is a species of four-legged, furry mammals that go “meow,” and we call such creatures “cats.”

Now, suppose I have an animal that I am trying to identify. It has four legs, is furry, is a mammal, and goes “meow.” It also happens to be white. My conclusion: it is a cat.

Now, suppose find another four-legged, furry, mewling mammal that happens to be black. Does the fact that it has a different color change the fact that it is a cat? No.

On the other hand, suppose I find another four-legged mammal. This time, however, it goes “woof.” My conclusion: this is a dog, not a cat. Even if it happens to be black or white in color, it would still be a dog.

So you see, in ordinary beings (what philosophers call “substances,” the things that stand by themselves, like animals, human beings, stones, and trees), certain characteristics pertain necessarily to the kind of thing it is (i.e., to its species). Others do not; they are (even in ordinary parlance) circumstantial.

Human acts (the technical term for actions that involve a moral or ethical decision) work in a similar way. Some of the characteristics of those acts are so central that they define the species (kind) of act. Others are not; they are merely circumstances.

Let’s take an example. Suppose I take money from the cashier at a grocery store. Is that wrong? Not necessarily.

Suppose I am taking the money out in order to give a customer his change. That is a good thing to do, obviously.

On the other hand, suppose I am taking the money in order to pocket it (and I am not authorized to do so; i.e., I am stealing it). That is not so good.

So, you see there is a “circumstance” here that actually determines the kind (species) of act that is being performed. (In this case, it even determines whether it is a good or an evil act.)

In your example, the thought remains impure regardless of how it arose. The species of act is “impure thought,” and the circumstance does not change that fact. (At least, assuming we mean the same thing by “impure thought,” which, it seems to me, is always sexual in nature.)

Does that make sense?

P.S. Although this is slightly off topic, I think it is important to point out that impure thoughts are only sinful if they are deliberate (that is, the person has to make an act of the will fostering them, or at least accepting them).

Hello TJ.

Yes. If you are busy flirting with a gal and it is the cause of sexual thoughts later on in the day, and you continue with those thoughts until you’ve sinned and take it to the Confessional, then both the number and species of sin must be mentioned. The the Priest will ask this: “Was the girl you were primarily involved in the flirtation that stimulated these thoughts married, engaged or single?” and depending on the actual conditions, the species of sin will change. It also matters if you are single, married or engaged or if you are attempting to live a religious life or aspiring to the Priesthood. Nothing can be hidden.

Hope that helps.


I wasn’t aware that those details were needed for sins of thought. I only thought state in life and the married, single etc mattered in impure acts. Thanks

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