What is aphasia?

Aphasia is a condition characterized by a loss of ability to understand or express speech, affecting an individual's capacity to communicate effectively. The correct response highlights the specific aspect of aphasia as an inability to speak, although it can also include difficulties with understanding, reading, and writing. This condition often arises from damage to language centers in the brain, commonly due to a stroke or traumatic injury.

The other answers relate to different concepts. Inability to articulate words clearly may describe a speech disorder but does not encompass the broader implications of aphasia. A severe allergic reaction refers to anaphylaxis and is unrelated to communication disorders. Controlled substance abuse concerns the misuse of drugs and is not connected to the language and speech difficulties that define aphasia. Therefore, recognizing aphasia as primarily an inability to speak is critical for understanding the condition and its impact on communication.