Mens Rea refers to the guilty mind required for criminal liability. Intention and recklessness are the two forms of Mens Rea that are part of most offences and have been the subject of judicial scrutiny. There is a vast volume of case law on intention and recklessness which demonstrates the problems that courts have had in perfecting an appropriate definition. Mens Rea is concerned with the defendants state of mind at the time of the Actus Reus. It is difficult to prove what was in someones mind which partially explains why the courts struggle with these words. Intention is the most culpable form of mens Rea.
This is because it is more blameworthy to cause harm deliberately (intention) than it is to do so carelessly (recklessness). Therefore intention is used in more serious offences. Murder requires intention to kill or cause GBH which sets it apart from other, less capable, forms of homicide. There is normally no need for an elaborate definition of intention in order to decide whether an Actus Reus was intended.
A few exceptional situations may present difficulty , but usually the analysis will be intuitively obvious. “The general legal opinion is that 'intention' cannot be satisfactorily defined and does not need a definition, since everybody knows what it means”. Lord Bridge in R v Moloney  AC 905, 926 states that “the golden rule should be that the judge should avoid any elaboration paraphrase of what is meant by intent, and leave it to the jury's good sense to decide whether the accused acted with the necessary intent”.
This is where the first form of intention, direct intention, falls under. Direct intention corresponds with the everyday meaning of intention. A person who has causing death as his aim, purpose or goal has direct intention to kill. It was defined in Mohan  as 'a decision to bring about the commission of an offence, no matter whether the defendant desired the consequences of his act or not.
Some cases are difficult which means that we do sometimes need guidelines about what intention means. The legal territory of intention comprises two alternative categories. D may be found to have intended the Actus Reus if I) D intended the Actus Reus in the ordinary, core sense of “intention”; or ii) D recognised that the Actus Reus was a virtually certain consequence of his actions.
The first case, is the standard or core variety and largely reflects the ordinary language meaning of “intention”. In this paradigm case, D tries to bring about the relevant outcome. For whatever reason, he wants or needs to bring about that outcome, and that is why he acts as he does. By contrast, in the virtual certainty case, (ii), D does not act in order to bring about the intended outcome. He acts for other reasons. However he knows that the Actus Reus is a virtually certain consequence of his actions. Though that is not what he is trying to bring about, it is a practically inevitable concomitant.
In very rare or exceptional cases, the result might not be D's aim or purpose. In such cases, D still might legally intend the result and so further direction to the jury is needed. This is where the second form of intention comes in, indirect/oblique intention. Glanville Williams (1987) described oblique intention as something you see clearly but out the corner of your eye, a side effect that you accept as an inevitable or 'certain' accompaniment of your direct intent. To be able to understand oblique intention in more depth, it is important to look at the progression of the case law that aided the development of indirect intention.
Moloney in the House of Lords: used 'natural consequences ' to describe something that necessarily followed the defendant's pursuit of his primary purpose. This was ambiguous as natural consequences need not be inevitable: pregnancy is a natural consequence of intercourse but it is by no means inevitable. Hancock and Shankland then addressed this ambiguity, stating that reference should be made to the degree of probability that the prohibited outcome would result from the defendant achieving his primary purpose.
Their reasoning was such that, the greater the probability of the consequence, the more likely it was that the result was foreseen, then the higher the level of foreseeability of the result and the more likely it was that the result was intended. Moloney, Hancock and Shankland conflicted in their formulation of an appropriate test of oblique intention. Nedrick in the court of Appeal addressed the conflict and formulated the virtual certainty test which conveyed inevitability (Moloney) and foreseeability (Hancock and Shankland). As Nedrick lacked the authoritative status of a House of Lords decision, subsequent case law eroded the narrow virtual certainty test.
In R v Woolin  the defendant threw his baby in exasperation when it would not stop crying. The baby died from head injuries. It was accepted that the defendant did not intend to cause harm to the child. His conviction for murder was upheld by the court of Appeal on the basis that it was not a misdirection to explain oblique intention to the jury in terms of 'appreciation of a substantial risk of injury'. His appeal was allowed by the House of Lords. Ultimately, the Court of Appeal in Woolin accepted a test based upon 'substantial risk' which created a dangerous overlap with recklessness (therefore blurring the line between murder and manslaughter).
However, in R v Matthews and Alleyne ( EWCA Crim 192,  2 Cr App R 30) the defendants appealed against their conviction for murder following the death of a young man (a non-swimmer) whom they had (having burgled) thrown from a bridge into a river. The Court of Appeal affirmed the conviction, which it did not consider unsafe in the light of the evidence, but expressed concern that the Nedrick/Woolin evidential rule should not be treated as if it were a rule of law. A defendant's foresight of virtually certain death does not automatically require the jury to find that he intended that result: it is merely (albeit often very strong evidence) from which the jury may infer intent.
In conclusion, it seems that when looking at oblique intention, there can be some confusion in the courts, however in my opinion, after some progression in this area following the cases of Woolin (1999) and Matthews (2003) the law of intention is satisfactorily defined in the criminal law.