Assertion (A): The criminal law does not take into account motive in affixing criminal liability or in determining criminal culpability.
Reasoning (R): If the act which is prohibited is done wilfully or knowingly then the same will cause liability in criminal law.

Both A and R are correct and R is not the correct explanation of A.

Intention or mental element is one of the foremost requirements in order to make someone liable for a crime. But a common misconception is that motive and intention are the same concepts when it comes to Crime. Thus, it is important to understand the fine distinction between these two terms. The meaning of doing an act intentionally in criminal law means something that is done wilfully and not accidentally or mistakenly. The person doing the act is well aware of the consequences or the outcomes of his action or omission. That is all what is required for affixing criminal liability. It does not matter, as we say in ordinary language, whether an act was done with good intent or bad intent. If the act which is prohibited (actus reus) is done wilfully, knowingly or with awareness of the resulting consequences then the same will cause liability in criminal law. Motive, on the other hand, is the ulterior objective behind doing an act. It is the driving force behind intention or commission of an act. The criminal law does not take into account motive in affixing criminal liability or in determining criminal culpability. This is the reason why the criminal law does not care whether one has stolen a loaf of bread to fed a starving person or stolen medicine to save someone's life, as long as it is a prohibited act, done knowingly.