General Antonyms:
* Reactive: This is the most direct antonym, meaning responding to situations after they occur rather than anticipating them.
* Passive: This implies a lack of initiative or involvement, waiting for things to happen instead of taking action.
* Inert: This implies a complete lack of action or response.
Other Possible Antonyms:
* Apathetic: This implies a lack of interest or concern.
* Indifferent: This implies a lack of care or feeling about a situation.
* Unresponsive: This implies a failure to react to stimuli.
* Complacent: This implies a sense of satisfaction with the status quo, leading to a lack of motivation for change.
The best antonym will depend on the specific situation and the nuance you want to convey.