Criminal intent question

There seem to be two established yet opposing principles of criminal law. One is Mens rea - Wikipedia, which says that there has to be an element of intentional wrongdoing to establish criminal culpability. But the other is Ignorantia juris non excusat - Wikipedia - usually phrased in English as “Ignorance of the law is no excuse”. So how is the line between these two principles drawn, especially in cases where someone thought they were acting within the law?

Here’s my non-lawyer guess: the criminal intent follow the intent to commit the act, said act which is illegal; however, a lack of actual knowledge of that act being illegal does not excuse one from criminal culpability.

Let me ask if I understand this right:

Suppose someone mistakenly thinks that marijuana is legal in Texas, and buys and smokes some. As such, the intent would be there - he intentionally used the marijuana - but the knowledge of it being illegal was absent - that’s what you mean?

You got it.

Correct. It’s the intention to do the action which is the mens rea component. For assault, for instance, it could be as as simple as « did the accused intend to hit the complainant? »

Now, if the statute in question adds particular qualifiers such as « wilfully », « knowingly », « for a corrupt purpose », or similar phrases, then the mens rea gets more complicated and there will be a more detailed analysis of mental intent tied to the statute’s wording.

ISTM that sometimes the act itself is defined by the intention.

Let’s suppose I see something lying in front of my house, assume it belongs to me or a family member, and bring it inside and put it in drawer. Turns out it belongs to a neighbor. I intended to take this object, I knew that theft is illegal, did I commit a theft?

Theft is a specific intent crime. It usually includes a phrase along the lines of « with intent to deprive the owner of the property ».

So, in your hypothetical, if the person who takes the object believed that it belongs to one of their own family and they’re just bringing it into their house, they don’t have the mens rea for theft.

But the mens rea isn’t personal knowledge of the terms of the statute. It’s a question whether the person intended to do the act defined by the statute as a crime.

This being so, it seems to me that the Latin phrase is a poor expression of the concept. It is not necessarily a “guilty mind”, since someone who is genuinely unaware of the illegality of the act (or who believes the law is immoral) will not feel guilt. It is simply the formation of intent.

Doesn’t matter if they don’t consider themselves guilty. Guilt is a legal finding by the court. Saying « I’m not guilty » doesn’t stop the bailiff from hauling you off once the court reaches a guilty verdict.

But in this case you intended to take a package that belonged to you into the house which is not an illegal act. You were just mistaken as to the nature of the package not of the law. Now if you knew the package was your neighbors and took it in anyway because you falsely believed thatfinders keepers was the law of the land then you’re in trouble.

Referring back to that wiki-
In some jurisdictions, there are exceptions to the general rule that ignorance of the law is not a valid defense. For example, under U.S. Federal criminal tax law, the element of willfulness required by the provisions of the Internal Revenue Code has been ruled by the courts to correspond to a “voluntary, intentional violation of a known legal duty” under which an “actual good faith belief based on a misunderstanding caused by the complexity of the tax law” is a valid legal defense. See Cheek v. United States.[12][13][14]

In Lambert v. California (1957), the Supreme Court of the United States ruled that a person who is unaware of a malum prohibitum law cannot be convicted of violating it if there was no probability he could have known the law existed. It was subsequently ruled in United States v. Freed (1971) that this exception does not apply when a reasonable person would expect their actions to be regulated, such as when possessing narcotics or dangerous weapons.[15]

So, altho intent is often include/codified in actual laws, afaik, ianal- "Ignorance of the law is no excuse” has not been so codified. In general, saying “I didn’t know murder was illegal” won’t work, but sometimes, if the law is obscure or very recent it can be a defense.