A patient understands speech but cannot verbalize their thoughts. What condition do they likely have?

The condition described in the question aligns with Broca's aphasia, which is characterized by the ability to comprehend speech while struggling to produce it. Individuals with Broca's aphasia typically have damage to the Broca's area of the brain, located in the frontal lobe, which is responsible for language production. This results in non-fluent, effortful speech, where the person may know what they want to say but finds it difficult to communicate those thoughts verbally.

In contrast, Wernicke's aphasia involves difficulty with comprehension, leading to fluent but nonsensical speech. Global aphasia represents a more severe form of language impairment where there is both an inability to understand speech and to produce understandable language. Anomic aphasia features intact comprehension but difficulty in retrieving words, which often leads to vague language or circumlocution.

Overall, the key characteristic of Broca's aphasia is the dissociation between understanding language and the ability to express oneself verbally, making it the most appropriate answer in this scenario.