TBA Law Blog

Posted by: Wade Davies on Nov 1, 2014

Journal Issue Date: Nov 2014

Journal Name: November 2014 - Vol. 50, No. 11

The doctrine sometimes called “diminished capacity” still seems to be confusing to practitioners and trial judges. I’d like to review the concept and offer some pointers on how defense counsel can develop relevant and admissible expert testimony regarding the mental state of the accused and how prosecutors can challenge such evidence.

The concept of diminished capacity is not esoteric. Crimes require proof of bad acts and mens rea. Most crimes require the State to prove beyond a reasonable doubt that the defendant had a certain mental state at the time of the act — usually intentional, knowing or reckless.[1] Premeditation is at issue in first-degree murder cases. When there is no question about who did the deed, defense counsel may want to show that because of a mental disease or defect, the defendant lacked the required mental element and is either not guilty or guilty of a lesser offense.

Challenging the mental state is distinct from insanity, which is an affirmative defense. “Diminished capacity” is not a defense; it is a rule that allows the admission of evidence of the defendant’s mental disease or defect in order to prevent the State from meeting its burden to prove the mental state in question.

In many criminal prosecutions, especially as technology advances, there is no question that the accused committed the act. The issue is whether the State can prove the required mental state. Let’s face it — many serious crimes are committed by people whose brains don’t work like yours and mine, and expert testing and testimony can assist the jury in determining guilt or the level of guilt.

Insanity has long been an available defense, but there are several problems with an insanity defense. First, the standard is hard to meet. The burden is on the defendant to prove by clear and convincing evidence that at the time of the offense a serious mental disease or defect prevented him from appreciating the nature or wrongfulness of the acts. Second, juries generally are not receptive to the idea that someone is “insane” and therefore not criminally responsible. It doesn’t work often — usually only when the defendant is so impaired that there is no question that there is no criminal responsibility. Next, the results of a verdict of not guilty by reason of insanity are not rosy for the defendant, who often ends up in a mental facility for longer than the sentence he or she would receive upon conviction

Sometimes then, defense counsel will want to argue that the defendant is not guilty of the charged offense not because of insanity but because she lacked the required intent.

There has been a great deal of confusion about “diminished capacity,” but a review of the case law shows ascertainable guidelines for developing or challenging expert testimony. Judge Penny White, then on the Court of Criminal Appeals, told us what diminished capacity is in State v. Phipps 20 years ago:

[D]iminished capacity is not a defense that absolves the accused from culpability; rather, it is a rule of evidence which allows the introduction of evidence to negate the existence of specific intent when a defendant is charged with a specific intent crime.[2]

Thus, diminished capacity is not technically a “defense.” It is a method of attacking the prosecution’s proof of the mental element.[3]

The Tennessee Supreme Court adopted Phipps a few years later in State v. Hall.[4] In Hall, the Supreme Court affirmed the exclusion of psychiatric testimony where the expert proposed to testify regarding the defendant’s personality type and character traits. The court made clear that the test for admissibility requires that the testimony be that the defendant lacks capacity:

While evidence that a particular defendant, because of a mental disease or defect, lacks the capacity to form the requisite intent is admissible in Tennessee, expert opinion testimony about the typical reactions of certain personality types is not relevant to the capacity of the particular defendant on trial.[5]

The court explained “diminished capacity” in depth. The main points from Hall are:

  1. The defendant must suffer from a recognized mental disease or defect.
  2. The disease or defect must cause the defendant to lack the capacity to form the required mental state.
  3. The expert testimony must otherwise satisfy the rules for admission of expert testimony.[6]

The court cited Phipps for the proposition that to exclude such testimony would deprive a defendant of the right to challenge an element of the offense.[7]

We probably should abandon the term “diminished capacity.” The Hall court directed that “[t]o avoid confusion …, we caution that such evidence should not be proffered as proof of ‘diminished capacity.’ Instead, such evidence should be presented to the trial court as relevant to negate the existence of the culpable mental state required to establish the criminal offense for which the defendant is being tried.”[8] I think the fact that courts have (correctly) emphasized that “diminished capacity” is not technically a defense may have contributed to some of the confusion about whether such evidence is admissible. My suggestion is to refer to it as Phipps/Hall evidence rather than “diminished capacity” to make sure to avoid confusion and to direct the court to the appropriate standard.

While Phipps addressed the negation of specific intent, the Supreme Court later made clear in State v. Ferrell that appropriate mental health testimony can also be used to rebut a showing of general intent.[9] Also, in Ferrell, the testimony did not deal with a psychiatric disorder but with a brain injury. The injury qualified as a mental defect.[10]

While courts have been careful to state that diminished capacity is not a “defense,” the Phipps/Hall standard has been incorporated into a pattern jury instruction that instructs jurors how to use and evaluate evidence of the defendant’s lack of capacity.[11]

Case law reflects a lot of failed attempts to develop and introduce capacity evidence. Notably, a number of cases have held that diminished capacity type evidence is not admissible unless the inability to premeditate is the result of a real mental disease or defect.[12] So the first step is to inquire whether the defendant has a disease or defect as opposed to a personality trait that tends to produce a certain reaction.

Recent cases show, though, that the most important factor for both defense counsel and prosecutors to remember is that the term “diminished” capacity is misleading. “Diminished” capacity is not sufficient; what is required is not diminished capacity but an incapacity to form the required intent. In some of the cases I’ve reviewed, the confusion seems to be based on the evaluator not knowing and being able to articulate the legal standard. At the very least, mental health professionals need to be advised of the correct standard before doing an evaluation.

A pair of recent Court of Criminal Appeals cases makes clear that mental health evidence is not admissible unless the evaluator can state that the defendant completely lacked the capacity to form the requisite intent. There does not appear to be room for nuance.

First, in State v. Merritt, the Court of Criminal Appeals affirmed the exclusion of a portion of a doctor’s opinion because the doctor could not say that the defendant completely lacked the capacity to premeditate.[13] There was no question that this defendant was seriously mentally ill. The defendant, also known as “Mad Max,” was refused service in a bar. He drew his pistol and killed the victim, resulting in his being served a beer and then charged with first degree murder. Merritt suffered from bipolar disorder, with psychotic features, polysubstance dependance, dementia, and a learning disability, with an IQ of 66. He also suffered from hallucinations. The doctor believed that the defendant’s ability to reflect and exercise judgment was “grossly impaired.”[14]

Nevertheless, the trial court excluded a portion of the psychiatric proof:

Dr. Murray again testified that he could not say within a reasonable degree of medical certainty that Defendant was suffering from PTSD on June 18, 2008. He also could not say within a reasonable degree of medical certainty that Defendant was incapable, because of his mental disease or defect, of premeditating the victim’s homicide. Dr. Murray agreed that he could not say within a reasonable degree of medical certainty that Defendant’s mental disease or defect rendered him incapable of committing a knowing and intentional killing.[15]

The evidence was that the mental disease or defect “impaired or reduced” his capacity to premeditate, not that it rendered him incapable.[16]

Because the court noted both the prosecutor and trial judge misunderstood the term diminished capacity, the Court of Criminal Appeals set out much of the history examined here.[17]

In May 2014, the Court of Criminal Appeals decided a case in which the psychologist stated that he could see a substantial impairment but could not say that the defendant completely lacked the capacity to premeditate.[18] The defendant’s capacity was “eroded” but the expert did not say it was “completely eroded.”[19]

As we have set out, the case law holds that expert testimony regarding a defendant’s mental state is relevant and admissible only to establish that, at the time of the crimes, the defendant lacked the capacity to premeditate. Since Dr. Kennon’s testimony did not do so, we conclude that the trial court erred in finding that the testimony was admissible. Accordingly, we reverse the order of the trial court in this regard.[20]

Although Merritt and Chaney are unpublished, they provide guidance to any practitioner who is considering having a client evaluated for capacity to form a certain mental state or for any prosecutor determining whether and how to object to such testimony. Most importantly, the expert must understand what he or she is being asked to evaluate. The expert should be given the appropriate standard based on Phipps/Hall. Further, the expert must understand the required mental state for the specific crimes alleged. The expert should be given a copy of Tenn. Code Ann. § 39-11-302 or the appropriate statute setting out the mental state.


  1. Tenn. Code Ann.  § 39-11-302.
  2. State v. Phipps, 883 S.W.2d 138, 143 (Tenn. Crim. App. 1994).
  3. David Raybin describes the doctrine as follows:
    Diminished capacity is not considered a justification or excuse for a crime, but rather an attempt to prove that the defendant, incapable of the requisite intent of the crime charged, is innocent of that crime but most likely guilty of a lesser-included offense. Thus, diminished capacity is actually a presentation of expert, psychiatric evidence aimed at negating the requisite culpable mental state. Properly understood, it is not a defense at all but merely a rule of evidence. To be admissible in a criminal prosecution, psychiatric testimony must demonstrate that the defendant’s inability to form the requisite culpable mental state was the product of a mental disease or defect and not just a particular emotional state or mental condition; it is the showing of lack of capacity to form the mental intent that is central to evaluating the admissibility of expert psychiatric testimony on the issue.
    § 28:20.Diminished capacity, 11 Tenn. Prac. Crim. Prac. & Procedure § 28:20 (citations omitted).
  4. State v. Hall, 958 S.W.2d 679, 690 (Tenn. 1997).
  5. Hall, 958 S.W.2d at 691.
  6. Hall, 958 S.W.2d at 689-90.
  7. Hall, 958 S.W.2d at 689-90.
  8. Hall, 958 S.W.2d at 690
  9. State v. Ferrell, 277 S.W.3d 372, 381 (Tenn. 2009)(holding that mental health proof should have been admitted during trial for escape).
  10. State v. Ferrell, 277 S.W.3d 372, 375 (Tenn. 2009).
  11. Tennessee Pattern Instruction, Criminal 42.22.
  12. See State v. Hatcher, 310 S.W.3d 788, 807 (Tenn. 2010)(“Defendant has cited us to no authority, however, for the proposition that simple fear is a sufficient mental disease or defect to require this jury instruction.”); State v. Faulkner, 154 S.W.3d 48, 57 (Tenn. 2005)(“Dr. Steinberg’s testimony was not offered to show that Faulkner lacked the capacity to form the requisite intent because of a mental disease or defect. His proposed testimony, therefore, did not meet the prerequisites of Hall.”); State v. Poole, W200700447CCAR3CD, 2009 WL 1025868 (Tenn. Crim. App. Apr. 14, 2009). (“In the instant case, Dr. Angelillo’s testimony was not offered to negate the requisite mental state, but to show that the appellant’s cognitive impairments impacted his ability to react appropriately in certain situations.”); State v. Vance, M2011-02469-CCA-R3CD, 2013 WL 6001954 (Tenn. Crim. App. Nov. 12, 2013), appeal denied (Apr. 10, 2014)(“However, we agree with the State that the thrust of Dr. Smith’s opinion went not to Defendant’s lack of capacity to form intent as a result of a mental disease or defect, but rather to Defendant’s diminished capacity as a result of intoxication. Therefore, we conclude that it was not error to exclude Dr. Smith’s testimony on the grounds that it fell outside the bounds of Hall and its progeny.”).
  13. State v. Merritt, E2011-01348-CCA-R3CD, 2013 WL 1189092 (Tenn. Crim. App. Mar. 22, 2013).
  14. Merritt, E2011-01348-CCA-R3CD, 2013 WL 1189092, slip. op. at 1, 22 (Tenn. Crim. App. Mar. 22, 2013).
  15. Merritt, E2011-01348-CCA-R3CD, 2013 WL 1189092, slip. op. at 22.
  16. Merritt, E2011-01348-CCA-R3CD, 2013 WL 1189092, slip. op. at 27.
  17. Merritt, E2011-01348-CCA-R3CD, 2013 WL 1189092, slip op. at 24-25.
  18. State v. Chaney, W2013-00914-CCA-R9CD, 2014 WL 2016655 (Tenn. Crim. App. May 14, 2014), appeal denied (Sept. 18, 2014).
  19. Chaney, W2013-00914-CCA-R9CD, 2014 WL 2016655, slip op. at 4, 9.
  20. Chaney, W2013-00914-CCA-R9CD, 2014 WL 2016655; see also, State v. Idellfonso-Diaz, M2006-00203-CCA-R9CD, 2006 WL 3093207 (Tenn. Crim. App. Nov. 1, 2006).

Wade Davies WADE DAVIES is the managing partner at Ritchie, Dillard, Davies & Johnson PC in Knoxville. He is a 1993 graduate of the University of Tennessee College of Law. The majority of his practice has always been devoted to criminal defense. Davies is a member of the Tennessee Bar Journal Editorial Board.