George Berkeley
George Berkeley also known as Bishop Berkeley (Bishop of Cloyne
Cloyne is a small town to the south-east of the town of Midleton in eastern County Cork, Province of Munster, Ireland. It is also a see city of the Anglican Diocese of Cork, Cloyne and Ross, while also giving its name to a Roman Catholic diocese...

), was an Irish
Irish may refer to:*Irish cuisine* Ireland, an island in north-western Europe, on which are located:** Northern Ireland, a constituent country of the United Kingdom** Republic of Ireland, a sovereign state...

 philosopher whose primary achievement was the advancement of a theory he called "immaterialism" (later referred to as "subjective idealism
Subjective idealism
Subjective idealism, or empirical idealism, is the monistic metaphysical doctrine that only minds and mental contents exist. It entails and is generally identified or associated with immaterialism, the doctrine that physical things do not exist...

" by others). This theory denies the existence of material substance
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

 and instead contends that familiar objects like tables and chairs are only idea
In the most narrow sense, an idea is just whatever is before the mind when one thinks. Very often, ideas are construed as representational images; i.e. images of some object. In other contexts, ideas are taken to be concepts, although abstract concepts do not necessarily appear as images...

s in the mind
The concept of mind is understood in many different ways by many different traditions, ranging from panpsychism and animism to traditional and organized religious views, as well as secular and materialist philosophies. Most agree that minds are constituted by conscious experience and intelligent...

s of perceivers
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...

, and as a result cannot exist without being perceived.

Our youth we can have but to-day,We may always find time to grow old.

Can Love be controlled by Advice?, reported in Bartlett's Familiar Quotations, 10th ed. (1919)

[Tar water] is of a nature so mild and benign and proportioned to the human constitution, as to warm without heating, to cheer but not inebriate.

Siris, paragraph 217. Compare: "Cups / That cheer but not inebriate", William Cowper, The Task, book iv, reported in Bartlett's Familiar Quotations, 10th ed. (1919)

That there is no such thing as what philosophers call material substance, I am seriously persuaded: but if I were made to see any thing absurd or skeptical in this, I should then have the same reason to renounce this, that I imagine I have now to reject the contrary opinion.

Philonous to Hylas

Doth the reality of sensible things consist in being perceived? or, is it something distinct from their being perceived, and that bears no relation to the mind?

Philonous to Hylas

Seeing therefore they are both [heat and pain] immediately perceived at the same time, and the fire affects you only with one simple, or uncompounded idea, it follows that this same simple idea is both the intense heat immediately perceived, and the pain;and consequently, that the intense heat immediately perceived, is nothing distinct from a particular sort of pain.

Philonous to Hylas

Since therefore, as well those degrees of heat that are not painful, as those that are, can exist in a thinking substance; may we not conclude that external bodies are absolutely incapable of any degree of heat whatsoever?

Philonous to Hylas. Hylas replies with, "So it seems."