prevenir

• prevenir follows venir: irregular first-person form
• prevenir follows venir: e → ie when the stem is stressed
• prevenir follows venir: irregular preterite stem; the 1s and 3s endings are unstressed, so they carry no written accent
• prevenir follows venir: irregular future stem; the endings themselves are regular
• prevenir follows venir: conditional shares the irregular future stem
• prevenir follows venir: present subjunctive is built from the irregular yo form
• prevenir follows venir: imperfect subjunctive is built from the third-person preterite stem
• e → i outside the present, where the stem is unstressed