some parts of several different and inconsistent ideas are put together'
ESSAY ON HUM. UNDERSTAND. B. iv. C. 7. S.9. This is the idea which he
thinks needful for the enlargement of knowledge, which is the subject of
mathematical demonstration, and without which we could never come to know
any general proposition concerning triangles. That author acknowledges it
doth 'require some pains and skill to form this general idea of a
triangle.' IBID. But had he called to mind what he says in another place,
to wit, 'That ideas of mixed modes wherein any inconsistent ideas are put
together cannot so much as exist in the mind, i.e. be conceived.' VID. B.
iii. C. 10. S. 33. IBID. I say, had this occurred to his thoughts, it is
not improbable he would have owned it above all the pains and skill he
was master of to form the above-mentioned idea of a triangle, which is
made up of manifest, staring contradictions. That a man who laid so great
a stress on clear and determinate ideas should nevertheless talk at this
rate seems very surprising. But the wonder will lessen if it be
considered that the source whence this opinion flows is the prolific womb
which has brought forth innumerable errors and difficulties in all parts
of philosophy and in all the sciences: but this matter, taken in its full
extent, were a subject too comprehensive to be insisted on in this place.
And so much for extension in abstract.

126. Some, perhaps, may think pure space, VACUUM, or trine dimension to
be equally the object of sight and touch: but though we have a very great
propension to think the ideas of outness and space to be the immediate
object of sight, yet, if I mistake not, in the foregoing parts of this
essay that hath been clearly demonstated to be a mere delusion, arising
from the quick and sudden suggestion of fancy, which so closely connects
the idea of distance with those of sight, that we are apt to think it is
itself a proper and immediate object of that sense till reason corrects
the mistake.