OPINION
STEWART, Judge.Ralph N. Wells lived in Salcha with Tina Woellert and her nine-month-old son, G.W. While Wells was caring for G.W., G.W. sustained numerous bruises on his head. A jury convicted Wells of third-degree assault (for recklessly causing G.W. physical injury that reasonably required medical treatment when Wells was 18 or older and G.W. was under 10 years of age).1 Based on this conviction, the superior court revoked Wells's probation on a prior conviction for removal of identification marks.2
Wells argues that there was insufficient evidence to conclude that Wells had recklessty caused G.W.'s injuries. Second, Wells argues that there was insufficient evidence that G.W.'s injuries reasonably required medical treatment. Wells argues that because there was insufficient evidence to support his conviction, the superior court erred when it revoked his probation.
Wells's first argument fails because the State presented circumstantial evidence that G.W. was in Wells's care when he was injured, that Wells persuaded Woellert not to take G.W. to the hospital the day he was injured, and that Wells's explanation of how GW. was injured was contradicted by the medical evidence. However, we accept Wells's second argument because the term "medical treatment" in AS is susceptible of more than one meaning, and under the meaning most favorable to Wells, the medical care that G.W. received was not "treatment." Accordingly, we must reverse Wells's third-degree assault conviction. Because we reverse Wells's conviction, the superior court must reconsider its decision to revoke Wells's probation.
Background facts and proceedings
On September 22, 2002, Wells called Woel-lert at her workplace and reported that G.W. had piled blankets and toys inside his crib to crawl out and had fallen out of the erib. Although Woellert thought that G.W. should go to the hospital, Wells convinced her that was unnecessary. Wells called Woellert back and told her that he had phoned a doctor at the hospital, and was told by the doctor that if G.W. was acting normally, it was not necessary to take him to the hospital. Wells also reported that the doctor recommended that he keep GW. awake for two hours, in case G.W. had a concussion, and that if G.W. fell asleep and stopped breathing, to administer CPR. When Woellert saw G.W. after work, she noticed "lots of bruises" on his head.
Woellert took G.W. to Fairbanks Memorial Hospital the next day. Dr. Sean Wormuth, an emergency room physician, examined G.W. Dr. Wormuth found numerous bruises on G.W.'s scalp, face, and ears. Dr. Wor-muth ordered a CT sean of G.W.'s head to check for any brain injury. In addition, Wormuth ordered lab tests to determine whether G.W.'s blood was clotting normally, or whether a bleeding disorder was causing the bruising. Dr. Wormuth contacted Dr. James Foote, another physician, to ensure that he would examine G.W. later to determine whether G.W. was healing properly. Foote examined G.W. two days later.
*974Was there sufficient evidence that Wells assqulted G.W.?
Wells argues that there was insufficient evidence to support the jury's finding that Wells had recklessly caused G.W.'s injuries. Viewing the evidence presented at trial in the light most favorable to upholding the verdict, the evidence is sufficient to support a conviction if fair-minded jurors could find the defendant guilty beyond a reasonable doubt.3
The State presented evidence that G.W. sustained the head injuries while in Wells's care. Woellert testified that she had not seen G.W. the morning of the incident, but that he was not bruised when she put him to bed the night before. Woellert also testified that Wells had elaimed that G.W. piled blankets and toys inside his crib to climb out and had fallen out of the crib. In addition, Woel-lert testified that, on the day G.W. was injured, Wells persuaded her not to take G.W. to the hospital.
Dr. Wormuth and Dr. Foote testified that G.W. was incapable of piling his belongings up in the crib to climb out, as Wells had claimed. Both doctors also testified that G.W.'s injuries were inconsistent with a fall from his erib. Dr. Wormuth explained that a fall from the crib could not have caused G.W.'s injuries because G.W. had bruises on every surface of his head. In contrast, a fall would injure only one side of the skull at a single point of impact. Also, because G.W.'s bruises were in differing stages of healing, he could not have sustained them in a single fall. Finally, Dr. Foote testified that G.W. could not have caused his head injuries by banging his head against his crib because he could not have generated enough foree to cause injuries as severe as those he had sustained. Because the State presented sufficient cireumstantial evidence that could have convinced a reasonable juror that Wells recklessly caused G.W.'s injuries, Wells's argument fails.
Did GW.'s injuries reasonably require medical treatment?
Wells argues that there was insuffi-client evidence to support the jury's finding that G.W.'s injuries reasonably required "medical treatment." Wells argues that because both Dr. Wormuth and Dr. Foote testified that they had determined G.W.'s bruises would heal naturally, medical treatment was not reasonably required.
If the answer to this question only required us to consider the sufficiency of the evidence presented, the answer is obvious because Dr. Wormuth testified that G.W.'s injuries required medical treatment.
But Wells actually raises a question that he did not present to the superior court. Wells moved for a judgment of acquittal after the State rested its case, but mentioned nothing concerning the failure to prove medical treatment. The jury instructions provided no definition of medical treatment. Wells did not object to the instructions, nor did he ask that the court define medical treatment.
During final argument, Wells contended that G.W. did not reasonably require medical treatment because the child's injuries "healed on their own," implying that medical treatment requires some form of remedy or active intervention. In rebuttal, the prosecutor discussed medical treatment.
Prosecutor: Medical treatment, what does medical treatment mean? Medical treatment means something different between lay people and doctors. When lay people think of medical treatment, they think of a cast. They think of a bandage. When a doctor thinks of medical treatment, it's broader than that. What did the doctors testify about what medical treatment meant to them? Medical treatment meant seeing the injury, analyzing the injury, diagnosis, x-rays, CAT seans, and then if any further treatment was necessary, then further treatment. CAT seans and x-rays, those things are medical treatment. That's what's meant by medical treatment. Did this baby need to go to the doctor? Yes. Did this baby need to be seen by a doctor, analyzed? Yes. Treated by a doctor? Yes. That's medical treatment. Just because the injuries heal without casts or surgery doesn't mean [that] it's not medical treatment.
*975Wells did not object to the prosecutor's discussion of medical treatment (nor has he claimed in this appeal that the prosecutor's argument misled the jury). Wells did not ask the court to provide any contrary or clarifying instruction to the jury on medical treatment before it retired to deliberate.
Immediately after the jury convicted Wells and was excused, Wells again moved for a judgment of acquittal, but did not assert that there was any deficiency regarding "medical treatment." If the jury needed a definition of "medical treatment," Wells could have requested an instruction. Because Wells made no objection to the instructions at trial, we review this question for plain error.
The evidence shows that the course of care that G.W. received was intended to promote G.W.'s physical health. When Dr. Wormuth saw G.W. in the emergency room, G.W. had numerous bruises on his sealp, face, and ears. Dr. Wormuth concluded that testing was warranted to examine whether there was any hemorrhaging in G.W.'s brain. G.W. was sedated intravenously to immobilize him for a CAT sean. Dr. Wormuth also ordered blood testing to check if G.W. had a blood disorder that exacerbated the bruising. Later, when Dr. Wormuth contacted Dr. Foote, the two physicians decided that G.W. was stable enough that he did not have to be admitted to the hospital. Instead, they scheduled a follow up with Dr. Foote in two days to make sure that G.W. was progressing.
Obviously, G.W. received more than first aid for his injuries. Dr. Wormuth concluded that G.W.'s injuries were of such magnitude that he needed to examine G.W. for internal bleeding and also make sure that his progress was monitored after he left the hospital.
Alaska Statute 11.41.220(a)(1)(C)(I) provides that a person commits third-degree assault if the person recklessly "while being 18 years of age or older ... causes physical injury to a child under 10 years of age and the injury reasonably requires medical treatment[.]" The legislature did not specifically define "medical treatment." Wells contends that to prove "medical treatment," the State must prove that the victim needs something more than medical attention.
In S.R.D.. v. State,4 a decision issued before the enactment of AS 11.41.220(2)(1)(C)(@), one of the appellants was convicted of three counts of criminal nonsupport. That appellant claimed that the evidence was insufficient to establish criminal nonsupport because the children did not require any medical treatment. However, the eriminal nonsupport statute penalizes a parent's failure to provide a child with necessary "medical attention."5 And we agreed with the State's argument that "medical attention" expressed a broader concept than "medical treatment." 6
We agree with the state that "attention" must be construed more broadly than "treatment." It is conceivable that children may suffer injuries sufficiently threatening to require a medical examination, even if that examination ultimately discloses no need for treatment.
In the present case, evidence concerning A.D.'s and S.E.D.'s injuries and the manner in which those injuries were inflicted was sufficient, when viewed in the light most favorable to the state, to permit a reasonable juror to infer that, even though no treatment was required, medical attention was actually necessary to rule out the possibility of life-threatening or potentially disabling conditions.[7]
When the legislature uses a word or phrase but does not define it, a court should normally assume that the legislature intended the word or phrase to have its common, ordinary meaning.8 The legislature has enacted other statutes that addressed the medical process. For example, in AS 18.20.1830(8), the legislature provided that " "hospital means an institution or establishment, public or private, devoted primarily to providing *976diagnosis, treatment, or care" (emphasis added). And in AS 25.20.025(a)(4), the legislature declared that all minors (even those who are unemancipated and who are still living with a parent or guardian) have the legal authority to consent to a broad range of medical services and treatments associated with sexual activity (exeept abortion), including "diagnosis, prevention or treatment of pregnancy, and ... diagnosis and treatment of venereal disease" (emphasis added). Additionally, in AS 47.17.290(7), the legislature provided that " 'institution' means a private or public hospital or other facility providing medical diagnosis, treatment, or care" (emphasis added).
Our supreme court recognized a similar distinction in the Rules of Evidence. Alaska Rule of Evidence 504(b) provides in part: "A patient has a privilege to refuse to disclose and to prevent any other person from disclosing confidential communications made for the purpose of diagnosis or treatment of the patient's physical, mental or emotional conditions" (emphasis added). And Evidence Rule 808(4) provides:
Statements for Purposes of Medical Diagnosis or Treatment. Statements made for purposes of medical diagnosis or treatment and describing medical history, or past or present symptoms, pain, or sensations, or the inception or general character of the cause or external source thereof insofar as reasonably pertinent to diagnosis or treatment.
(Emphasis added.)
In case law, our supreme court has also used the terms "diagnosis" and "treatment" as expressing different steps in the medical process. For example, in Bradbury v. Chugach Electric Ass'n,9 the court stated: "Two physicians, Dr. Kenueth Flora and Dr. David Nelson, testified on behalf of Chugach Electric. Dr. Flora is a hepatologist whose sub-specialty is the diagnosis and treatment of chronic liver disease.10
When the seope of a eriminal statute is unclear, courts should normally construe the statute against the government-that is, construe it so as to limit the seope of criminal liability.11 And when a word or phrase has been construed in a particular way-as we construed the word "treatment" in S.R.D. v. State-courts are to presume that later-enacted statutes carry forward the existing judicial construction of that word or phrase.
At best, the construction of "medical treatment" in the statute that is endorsed by the State, and the construction that was advocated by the prosecutor in summation to the jury, is only arguable. We therefore must interpret the statute against the government.12 Accordingly, we conclude that we must reverse Wells's conviction.
If the State elects not to re-prosecute Wells for third-degree assault, the superior court may enter judgment against Wells for fourth-degree assault13 because the jury's verdict necessarily found that Wells had recklessly caused physical injury to the victim.14
Why we vacate the superior court's revocation of Wells's probation
The superior court revoked Wells's probation in his conviction for removal of identification marks because he was convicted of third-degree assault in this case. Because we reversed Wells's third-degree assault conviction, we vacate the probation revocation.
However, as we discussed above, the jury necessarily found that Wells recklessly caused physical injury to GW. That jury finding is sufficient to support a conviction *977for fourth-degree assault. In addition, this jury finding would be sufficient for the superior court to exercise its discretion to revoke Wells's probation. Accordingly, we direct the superior court to reconsider the petition to revoke Wells's probation.
Conclusion
The judgment of the superior court is REVERSED.
. AS 11.41.220(a)(1)(C)@).
. AS 11.46.260(a).
. See Dorman v. State, 622 P.2d 448, 453 (Alaska 1981).
. $20 P.2d 1088 (Alaska App.1991).
. AS 11.51.120(b).
. S.R.D., 820 P.2d at 1090.
7. Id. at 1090-91.
. See AS 01.10.040; Lynch v. McCann, 478 P.2d 835, 837 (Alaska 1970); Lambert v. State, 694 P.2d 791, 793 (Alaska App.1985).
. 71 P.3d 901 (Alaska 2003).
. Id. at 905.
. See State v. ABC Towing, 954 P.2d 575, 579 (Alaska App.1998); Magnuson v. State, 843 P.2d 1251, 1253 (Alaska App.1992).
. See Brookins v. State, 600 P.2d 12, 17 (Alaska 1979); Whitesides v. State, 88 P.3d 147, 151 (Alaska App.2004); State v. Andrews, 707 P.2d 900, 907 (Alaska App.1985); State v. Rastopsoff, 659 P.2d 630, 640 (Alaska App.1983).
. AS 11.41.230(a)(1).
. See Nathaniel v. State, 668 P.2d 851, 857 n. 4 (Alaska App.1983); Nix v. State, 624 P.2d 823, 824-25 (Alaska App.1981).