However, for idealists they aren’t fazed by this problem because the philosophy idealism states that there are no physical objects behind the sense data we perceive anyway. Therefore, when an idealist is looking at the table, all they are seeing is the sense data of the table. Since there is no physical object behind the sense data of the table, then idealists won’t have to face the linking problem. An ‘object’, according to Berkeley, is simply a bundle of ideas with no physical existence independent of sensation.
Furthermore, another strength to idealism is its ability to overcome the problem of material substance. In order to argue that physical objects are independent of our minds, we need the idea of material substance. Philosopher John Locke argued that primary and secondary qualities belonged to the physical object. The properties of the object are ‘held together’ by its material substance – matter. It is due to physical objects having substance, that they can exist unperceived. When I looks at a table, the only thing I see are its qualities e.g. its shape, colour, size etc. However, if I took each of these qualities away, one by one, then there would be nothing left to see. Hence what is the point of suggesting a ‘material substance’; that binds all the qualities of a physical object, if it possibly doesn’t even exist anyway once you remove all the qualities? Locke saw the point, and accepted that material substance was unknowable.
On the other hand, Berkeley’s idealism solves the need for talking about the material substance of physical objects: because for him they are nothing more than the ideas we perceive, existing together as a bundle. For example when we see a table, we just perceive a bundle of qualities e.g. shape, colour, size etc, rather than an actual physical object. He objected that realists didn’t really know what they were talking about, or even if they were talking sense, in talking about a material substance. Instead he argued that what we experience when we experience qualities, either primary or secondary, are ideas; and ideas only exist in the mind. It doesn’t make sense to say a pain exists unless someone feels it, or that a colour exists unless someone sees it. Nor does it make any sense to say a shape exists unless someone sees or feels it. For example; what is the shape ‘square’ except what we see or feel? We can only make sense of it as our experience of square.
However, there are quite a few criticisms that Berkeley’s ‘esse est percipi’ faces. One such difficulty for idealism is dealing with illusions. Berkeley has argued that we can tell the difference between imagination and perception by voluntariness and regularity. Yet, illusions are no more voluntary than perceptions, and can be perfectly regular and natural. For example a stick looks bent half-submerged in water and a red rose looks grey under sodium light etc. How is it possible that the stick can be both bent and not bent? Berkeley’s response is that we aren’t misperceiving, but rather the stick is bent when half-submerged. However, this is misleading since it is essentially implying that the stick would remain being bent when pulled out of the water. Therefore, we shouldn’t say ‘the stick is bent’, since this means it would remain so under normal conditions; bur rather the intuitive thing to say is that ‘the stick looks bent’, which would be the correct way of saying it.
Another problem to Berkeley’s idealism is that there are possibly simpler, more systematic alternatives to idealism, in regards to explanation of our sense data; e.g. Bertrand Russell’s cat analogy. If the cat exists independently of us then we can understand why its sense data is able to move from one place to another, and why it gets hungry between meals. However, if it just a collection or bundle of sense-data, then it is harder for idealists to explain why this is. Berkeley response to this criticism is that our sense data are caused by God, and he perceives all, so even when we don’t perceive the cat, it continues to exists because God still perceives it. But this response then seems to imply that God perceives things in the same way as we do, which seems very unlikely. Also, ordinary objects change and go out of existence, so they cannot be ideas in a mind that is unchanging and eternal. If they were, then this would cause problems immutability. In addition to this, the whole response itself brings up the massive debate of God’s existence anyway, making it even weaker.
In conclusion, the weakness to Berkeley’s ‘esse est percipi’ (to be is to be perceived) - outweigh the strengths. There are indeed a few strengths to idealism, such as it being able to overcome the linking problem, which is a major challenge to realism, and also the problem of material substance, since idealists believe that there is nothing behind the sense-data we perceive. However there are quite a few strong arguments against idealism as well, such as the problem of illusions, where idealists face the problem of being unable to differentiate between veridical perception and illusions. Finally, there are simpler, more systematic alternatives for explaining sense data which appeals to basic common sense.