The self is an individual person as the object of his or her own reflective consciousness. The self has been studied extensively by philosophers and psychologists and is central to many world religions.

The philosophy of self seeks to describe essential qualities that constitute a person's uniqueness or essential being. There have been various approaches to defining these qualities. The self can be considered that being which is the source of consciousness; the agent responsible for an individual's thoughts and actions; and/or the substantial nature of a person which endures and unifies consciousness over time.

The philosophy of a disordered self, such as in schizophrenia, is described in terms of what the psychiatrist understands are actual events in terms of neuron excitation but are delusions nonetheless, and the schizo-affective or schizophrenic person also believes are actual events in terms of essential being. PET scans have shown that auditory stimulation relates to certain areas of the brain and imagined similar events occur in adjacent areas but hallucinations occur in the same areas. In such cases, external influences may be the source of consciousness and the person may or may not be responsible for "sharing" in the mind's process; and/or the events which occur, such as visions and auditory stimuli, may endure and be repeated often over hours, days, months or years -- and the afflicted person may believe themselves to be in a state of rapture and/or possession, which their artistic expression may tend to confirm. Whether art has moral responsibility is difficult to relate to the idea of a unique source of consciousness and rapid thinking may lead to an insubstantial nature of the enduring person's consciousness over time; it can be said in view of these two exigencies that the person is vulnerable.

An adhesive or stick on is a material, usually in a liquid or semi-liquid state, that adheres or bonds items together. Adhesives come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials. Adhesives cure (harden) by either evaporating a solvent or by chemical reactions that occur between two or more constituents.

Adhesives are advantageous for joining thin or dissimilar materials, minimizing weight, and when a vibration-damping joint is needed. A disadvantage of most adhesives is that most do not form an instantaneous joint, unlike many other joining processes, because the adhesive needs time to cure.

The earliest known date for a simple glue is 200,000 BC and for a compound glue 70,000 BC.

The oldest known adhesive, dated to approximately 200,000 BC, is from spear stone flakes glued to a wood with birch-bark-tar, which was found in central Italy. The use of compound glues to haft^{[clarification needed]} stone spears into wood dates back to approximately 70,000 BC. Evidence for this has been found in Sibudu Cave, South Africa and the compound glues used were made from plant gum and red ochre. The Tyrolean Iceman had weapons fixed together with the aid of birch-bark-tar glue.