Aphthous Ulcers: These are the most common cause of painful ulcers on the tongue and elsewhere in the oral cavity. They are benign, recurrent, and can be triggered by stress, trauma, or certain foods.

Traumatic Ulcers: These can occur due to accidental biting of the tongue, sharp edges of teeth, or dental appliances, leading to painful ulcers.
Oral Lichen Planus: An autoimmune condition that can cause white patches and painful ulcers in the mouth, including on the tongue.
Recurrent Herpes Simplex Infection: Although more commonly associated with the lips (cold sores), herpes simplex can also cause ulcers on the tongue, especially in immunocompromised individuals.

Squamous Cell Carcinoma: Although rare, any persistent or non-healing ulcer, especially in smokers or those with a history of alcohol abuse, should raise suspicion for oral cancer.
Syphilis: Secondary syphilis can cause mucous patches or ulcers in the mouth, which can be painful.
HIV-Related Ulcers: Individuals with HIV/AIDS can develop oral ulcers due to various opportunistic infections or as a direct result of the immunocompromised state.

Erythema Multiforme: A rare skin condition that can also affect the mucous membranes, causing ulcers, including on the tongue.
Pemphigus Vulgaris: An autoimmune disease that can cause blisters and ulcers in the mouth, including on the tongue, though it's more common in older adults.
Behçet's Disease: A form of vasculitis that can cause oral ulcers, among other symptoms, though it's relatively rare and often associated with other systemic symptoms.